s390/bpf: Enable arena

Now that BPF_PROBE_MEM32 and address space cast instructions are
implemented, tell the verifier that the JIT supports arena.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240701234304.14336-9-iii@linux.ibm.com