s390/checksum: support GENERIC_CSUM, enable it for KASAN

This is the s390 variant of commit d911c67e ("x86: kasan: kmsan:
support CONFIG_GENERIC_CSUM on x86, enable it for KASAN/KMSAN"). Even
though most of the s390 specific checksum code is written in C there is
still the csum_partial() inline assembly which could prevent KASAN and
KMSAN from seeing all memory accesses.

Therefore switch to GENERIC_CSUM if KASAN is enabled just like x86.

Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>