Implement sendfile(2) for the posix shared memory segment file descriptor,
in addition to the regular files.

Requested by:	alc
Discussed with:	emaste
Tested by:	pho (previous version)
Sponsored by:	The FreeBSD Foundation
Approved by:	re (hrs)
Cleanup elf macros

Only define EF_MIPS_ABI when not already supplied
Remove old now unused ARM macros

Reported by:	imp
Approved by:	re (kib)
Fix a limitation in bhyve that would limit the number of virtual machines to
the maximum number of VT-d domains (256 on a Sandybridge). We now allocate a
VT-d domain for a guest only if the administrator has explicitly configured
one or more PCI passthru device(s).

If there are no PCI passthru devices configured (the common case) then the
number of virtual machines is no longer limited by the maximum number of
VT-d domains.

Reviewed by: grehan@
Approved by: re@