KVM: x86: Mask off reserved bits in CPUID.80000006H

KVM_GET_SUPPORTED_CPUID should only enumerate features that KVM
actually supports. CPUID.80000006H:EDX[17:16] are reserved bits and
should be masked off.

Fixes: 43d05de2 ("KVM: pass through CPUID(0x80000006)")
Signed-off-by: Jim Mattson <jmattson@google.com>
Message-Id: <20220929225203.2234702-2-jmattson@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>