s390: enable bpf jit by default when not built as always-on

This is the s390 variant of commit 81c22041

 ("bpf, x86, arm64:
Enable jit by default when not built as always-on").

Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>