selftests: KVM: s390x: Add reset tests

Test if the registers end up having the correct values after a normal,
initial and clear reset.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Link: https://lore.kernel.org/r/20200131100205.74720-6-frankja@linux.ibm.com


Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>