x86/access: Print the index when dumping PTEs

Print the index of a PTE in addition to its level.  If there's a test bug
that causes an unwanted collision, the index is critical information to
understanding what has gone wrong.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211125012857.508243-13-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>