x86: access: Add tests for reserved bits of guest physical address

This extends the access tests to also test for reserved bits
in guest physical addresses.

Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
Message-Id: <20200423103623.431206-1-mgamal@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>