KVM: s390: selftests: Use TAP interface in the memop test

KVM: s390: selftests: Use TAP interface in the memop test

The memop test currently does not have any output (unless one of the
TEST_ASSERT statement fails), so it's hard to say for a user whether
a certain new sub-test has been included in the binary or not. Let's
make this a little bit more user-friendly and include some TAP output
via the kselftests.h interface.

Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Link: https://lore.kernel.org/r/20220531101554.36844-2-thuth@redhat.com
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>