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

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

The tprot 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>
Reviewed-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Link: https://lore.kernel.org/r/20220531101554.36844-4-thuth@redhat.com
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>