KVM: selftests: Verify KVM stuffs runtime CPUID OS bits on CR4 writes

KVM: selftests: Verify KVM stuffs runtime CPUID OS bits on CR4 writes

Extend x86's set sregs test to verify that KVM sets/clears OSXSAVE and
OSKPKE according to CR4.XSAVE and CR4.PKE respectively.  For performance
reasons, KVM is responsible for emulating the architectural behavior of
the OS CPUID bits tracking CR4.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20241128013424.4096668-10-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>