x86/cpuid: leak OSXSAVE only when XSAVE is not clear in policy

x86/cpuid: leak OSXSAVE only when XSAVE is not clear in policy

This fixes booting of old non-PV-OPS kernels which historically
looked for OSXSAVE instead of XSAVE bit in CPUID to check whether
XSAVE feature is enabled. If such a guest appears to be started on
an XSAVE enabled CPU and the feature is explicitly cleared in
policy, leaked OSXSAVE bit from Xen will lead to guest crash early in
boot.

Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>