Fixthe spelling of ehci
Revert rr271190, it was based on a misunderstanding.  The problem of
non-existant device<->xref info needs to be handled by creating the info,
which will come in a subsequent commit.
o Remove __unused attribute on variables which actually used
o Unmagic 'configuration done' bit
o Move probe() to place before attach() for better navigation
o Use bus_read_n instead of bus_space_read_n functions

Pointed out by:	andrew
Sponsored by:	DARPA, AFRL
Restore order of interrupt setup. Minor problems can result by
setting up the interrupts too early:

Reviewed by: mav@
Sponsored by: Netflix
When registering an association between a device and an xref phandle, create
an entry in the xref list if one doesn't already exist for the given handle.

On a system that uses phandle properties, the init-time scan of the tree
which builds the xref list will pre-create entries for every xref handle
that exists in the data.  On systems where the xref and node handles are
synonymous there is no phandle property in referenced nodes, and the xref
list will initialize to an empty state.  In the latter case, we still need
to be able to associate a device_t with an xref handle, so we create list
entries on the fly as needed.  Since the node and xref handles are
synonymous, we have all the info needed to create a list entry at device
registration time.

The downside to this change is that it basically allows on the fly creation
of xref handles as synonyms of node handles, and the association of a
device_t with them.  Whether this is a bug or a feature is in the eye of
the beholder, I guess.
Fix the handling of sysctl variables when used with VIMAGE.
While there do some cleanup of the code.

MFC after: 1 week
SDM rev. 50 defines the use of the next 8 bytes in the xstate header.
It is the compaction bitmask, with the highest bit defining if compact
format of the xsave area is used at all.

Adjust the definition of struct xstate_hdr, provide define for bit 63.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Save one register read (AHCI_IS) for AHCI controllers with only one port.

For controllers with only one port (like PCIe or M.2 SSDs) interrupt can
come from only one source, and skipping read saves few percents of CPU time.

MFC after:	1 month
H/W donated by:	I/O Switch
Add a define for index of IA32_XSS MSR, which is, per SDM rev. 50, an
analog of XCR0 for ring 0 FPU state, used by XSAVES and XRSTORS.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Fix a leak of an address, if the address is scheduled for removal
and the stack is torn down.
Thanks to Peter Bostroem and Jiayang Liu from Google for reporting the
issue.

MFC after: 1 week