KVM: x86: optimize check for valid PAT value

[ Upstream commit 674ea351cdeb01d2740edce31db7f2d79ce6095d ]

This check will soon be done on every nested vmentry and vmexit,
"parallelize" it using bitwise operations.

Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>