nSVM: Add test for NPT reserved bit and #NPF error code behavior

Add a test to verify that KVM generates the correct #NPF and PFEC when
host and guest EFER.NX and CR4.SMEP values diverge, and that KVM
correctly detects reserved bits in the first place.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210622210047.3691840-13-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>