x86: Fix "x86: further CPUID handling adjustments"

x86: Fix "x86: further CPUID handling adjustments"

c/s f9616884e (a backport of c/s 0d703a701 "x86/feature: Definitions for
Indirect Branch Controls") missed a CPUID adjustment when calculating the raw
featureset.  This impacts host administrator diagnostics.

Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
c/s 62b187969 "x86: further CPUID handling adjustments" make some adjustments.
However, it breaks levelling of guests, making it impossible for the toolstack
to hide STIBP or IBPB from guests on hardware with up-to-date microcode.

The dom0 issue referenced in the commit message was fixed by the hunk
adjusting the zeroing alone.  STIBP and IBPB don't need (and indeed, must not
be for levelling purposes) OR'd into the leaf.

One final item which was missed in backport was the need to ignore the
toolstack choice of STIBP, and set it equal to IBRSB.  This needs doing after
the mask has been applied.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Gbp-Pq: Name x86-fix-x86-further-cpuid-handling-adjus.patch