x86/xsave: enable support for new ISA extensions

x86/xsave: enable support for new ISA extensions

Intel has released a new version of Intel Architecture Instruction Set
Extensions Programming Reference, adding new features like AVX-512,
MPX, etc. Refer to
http://download-software.intel.com/sites/default/files/319433-015.pdf

This patch adds support for these new instruction set extensions
without enabling this support for guest use, yet.

It also adjusts XCR0 validation, at once fixing the definition of
XSTATE_ALL (which is not supposed to include bit 63).

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Acked-by: Keir Fraser <keir@xen.org>