Tidy up some loose ends in the PCID code:

- Restore the pre-PCID TLB shootdown handlers for whole address space
  and single page invalidation asm code, and assign the IPI handler to
  them when PCID is not supported or disabled.  Old handlers have
  linear control flow.  But, still use the common return sequence.

- Stop using pcpu for INVPCID descriptors in the invlrg handler.  It
  is enough to allocate descriptors on the stack.  As result, two
  SWAPGS instructions are shaved off from the code for Haswell+.

- Fix the reverted condition in invlrng for checking of the PCID
  support [1], also in invlrng check that pmap is kernel pmap before
  performing other tests.  For the kernel pmap, which provides global
  mappings, the INVLPG must be used for invalidation always.

- Save the pre-computed pmap' %CR3 register in the struct pmap.  This
  allows to remove several checks for pm_pcid validity when %CR3 is
  reloaded [2].

Noted by:   gibbs [1]
Discussed with:	alc [2]
Tested by:	pho, flo
Sponsored by:	The FreeBSD Foundation
Correct blkback handling of the BLKIF_OP_FLUSH_DISKCACHE opcode.

Properly round-trip the "operation code" for client requests.

sys/dev/xen/blkback/blkback.c:
	In xbb_dispatch_dev() when processing a flush request,
	correctly set bio->bio_caller1 to the request list (not
	bare request) for the operation, as is expected by the
	completion handler xbb_bio_done().

	In xbb_get_resources(), initialize "operation" in the
	driver's internal request object from the client's "ring
	request", so it is correct when used to populate the reply
	when this operation completes.

Submitted by:	Roger Pau Monné
Sponsored by:	Citrix Systems R&D
Reviewed by:	gibbs
Change the cap_rights_t type from uint64_t to a structure that we can extend
in the future in a backward compatible (API and ABI) way.

The cap_rights_t represents capability rights. We used to use one bit to
represent one right, but we are running out of spare bits. Currently the new
structure provides place for 114 rights (so 50 more than the previous
cap_rights_t), but it is possible to grow the structure to hold at least 285
rights, although we can make it even larger if 285 rights won't be enough.

The structure definition looks like this:

	struct cap_rights {
		uint64_t	cr_rights[CAP_RIGHTS_VERSION + 2];
	};

The initial CAP_RIGHTS_VERSION is 0.

The top two bits in the first element of the cr_rights[] array contain total
number of elements in the array - 2. This means if those two bits are equal to
0, we have 2 array elements.

The top two bits in all remaining array elements should be 0.
The next five bits in all array elements contain array index. Only one bit is
used and bit position in this five-bits range defines array index. This means
there can be at most five array elements in the future.

To define new right the CAPRIGHT() macro must be used. The macro takes two
arguments - an array index and a bit to set, eg.

	#define	CAP_PDKILL	CAPRIGHT(1, 0x0000000000000800ULL)

We still support aliases that combine few rights, but the rights have to belong
to the same array element, eg:

	#define	CAP_LOOKUP	CAPRIGHT(0, 0x0000000000000400ULL)
	#define	CAP_FCHMOD	CAPRIGHT(0, 0x0000000000002000ULL)

	#define	CAP_FCHMODAT	(CAP_FCHMOD | CAP_LOOKUP)

There is new API to manage the new cap_rights_t structure:

	cap_rights_t *cap_rights_init(cap_rights_t *rights, ...);
	void cap_rights_set(cap_rights_t *rights, ...);
	void cap_rights_clear(cap_rights_t *rights, ...);
	bool cap_rights_is_set(const cap_rights_t *rights, ...);

	bool cap_rights_is_valid(const cap_rights_t *rights);
	void cap_rights_merge(cap_rights_t *dst, const cap_rights_t *src);
	void cap_rights_remove(cap_rights_t *dst, const cap_rights_t *src);
	bool cap_rights_contains(const cap_rights_t *big, const cap_rights_t *little);

Capability rights to the cap_rights_init(), cap_rights_set(),
cap_rights_clear() and cap_rights_is_set() functions are provided by
separating them with commas, eg:

	cap_rights_t rights;

	cap_rights_init(&rights, CAP_READ, CAP_WRITE, CAP_FSTAT);

There is no need to terminate the list of rights, as those functions are
actually macros that take care of the termination, eg:

	#define	cap_rights_set(rights, ...)				\
		__cap_rights_set((rights), __VA_ARGS__, 0ULL)
	void __cap_rights_set(cap_rights_t *rights, ...);

Thanks to using one bit as an array index we can assert in those functions that
there are no two rights belonging to different array elements provided
together. For example this is illegal and will be detected, because CAP_LOOKUP
belongs to element 0 and CAP_PDKILL to element 1:

	cap_rights_init(&rights, CAP_LOOKUP | CAP_PDKILL);

Providing several rights that belongs to the same array's element this way is
correct, but is not advised. It should only be used for aliases definition.

This commit also breaks compatibility with some existing Capsicum system calls,
but I see no other way to do that. This should be fine as Capsicum is still
experimental and this change is not going to 9.x.

Sponsored by:	The FreeBSD Foundation
Regenerate after r255219.

Sponsored by:	The FreeBSD Foundation
Style fixes. Most fixes are about not treating integers and pointers as
booleans.
Style fixes.