target/s390x: Make CKSM raise an exception if R2 is odd

target/s390x: Make CKSM raise an exception if R2 is odd

R2 designates an even-odd register pair; the instruction should raise
a specification exception when R2 is not even.

Cc: qemu-stable@nongnu.org
Fixes: e023e832d0ac ("s390x: translate engine for s390x CPU")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230724082032.66864-2-iii@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>