Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Upgrade Xen interface headers to Xen 4.2.1.

Move FreeBSD from interface version 0x00030204 to 0x00030208.
Updates are required to our grant table implementation before we
can bump this further.

sys/xen/hvm.h:
Replace the implementation of hvm_get_parameter(), formerly located
in sys/xen/interface/hvm/params.h. Linux has a similar file which
primarily stores this function.

sys/xen/xenstore/xenstore.c:
Include new xen/hvm.h header file to get hvm_get_parameter().

sys/amd64/include/xen/xen-os.h:
sys/i386/include/xen/xen-os.h:
Correctly protect function definition and variables from being
included into assembly files in xen-os.h

Xen memory barriers are now prefixed with "xen_" to avoid conflicts
with OS native primatives. Define Xen memory barriers in terms of
the native FreeBSD primatives.

Sponsored by: Spectra Logic Corporation
Reviewed by: Roger Pau Monné
Tested by: Roger Pau Monné
Obtained from: Roger Pau Monné (bug fixes)

Update xen/interface includes to the latest in mercurial

MFC after: 1 month

partial update to interface headers to 3.2

MFC after: 1 month

Import OS interfaces to Xen services.

MFC after: 2 weeks