KVM: x86: add support for CPUID leaf 0x80000021

Commit 58b3d12c upstream.

CPUID leaf 0x80000021 defines some features (or lack of bugs) of AMD
processors.  Expose the ones that make sense via KVM_GET_SUPPORTED_CPUID.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>