xen: move grant table code

Mave the grant table code into the dev/xen folder in preparation for turning
it into a device using the newbus interface. This is just code motion, no
functional changes.

Sponsored by: Citrix Systems R&D
o Put () for p to avoid unexpected macro expansion
o style(9) fix

Submitted by:	Yonghyeon PYUN <pyunyh@gmail.com>
xen: convert the Grant-table code to a NewBus device

This allows the Grant-table code to attach directly to the xenpv bus,
allowing us to remove the grant-table initialization done in xenpv.

Sponsored by: Citrix Systems R&D
xen: mask event channels while binding them to a vCPU

Mask the event channel source before trying to bind it to a CPU, this
prevents stray interrupts from firing while assigning them and hitting the
KASSERT in xen_intr_handle_upcall.

Sponsored by: Citrix Systems R&D
xen/intr: balance dynamic interrupts across available vCPUs

By default Xen binds all event channels to vCPU#0, and FreeBSD only shuffles
the interrupt sources once, at the end of the boot process. Since new event
channels might be created after this point (because new devices or backends
are added), try to automatically shuffle them at creation time.

This does not affect VIRQ or IPI event channels, that are already bound to a
specific vCPU as requested by the caller.

Sponsored by: Citrix Systems R&D
Add fstyp(8).  This utility, named after its SVR4 counterpart, detects
filesystems.  It differs from file(1) in that it gives machine-parseable
output, it outputs filesystem labels, doesn't get confused by other
formats metadata, and runs in Capsicum sandbox.

Differential Revision:	https://reviews.freebsd.org/D1255
Relnotes:	yes
Sponsored by:	The FreeBSD Foundation
Add "-media" autofs map, to access data on removable media, such as CD
drives or flash keys.  It can be enabled by uncommenting a single entry
in default /etc/auto_master.  It can also be easily modified to use
fuse-based filesystems instead of in-kernel ones.

There is still one deficiency - the mountpoints are permanent, they
don't disappear when user removes the media.  Fixing it needs some
autofs changes.

Differential Revision:	https://reviews.freebsd.org/D1210
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Fix a typo reported by Lennart Grahl.

MFC after: 3 days