x86/xsaves: Detect xsaves/xrstors feature

Detect the xsaveopt, xsavec, xgetbv, and xsaves features in processor extended
state enumberation sub-leaf (eax=0x0d, ecx=1):
Bit 00: XSAVEOPT is available
Bit 01: Supports XSAVEC and the compacted form of XRSTOR if set
Bit 02: Supports XGETBV with ECX = 1 if set
Bit 03: Supports XSAVES/XRSTORS and IA32_XSS if set

The above features are defined in the new word 10 in cpu features.

The IA32_XSS MSR (index DA0H) contains a state-component bitmap that specifies
the state components that software has enabled xsaves and xrstors to manage.
If the bit corresponding to a state component is clear in XCR0 | IA32_XSS,
xsaves and xrstors will not operate on that state component, regardless of
the value of the instruction mask.

Signed-off-by: Fenghua Yu <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: H. Peter Anvin <[email protected]>

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