s390/bpf: Remove JITed image size limitations

Now that jump and long displacement ranges are no longer a problem,
remove the limit on JITed image size. In practice it's still limited by
2G, but with verifier allowing "only" 1M instructions, it's not an
issue.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191118180340.68373-7-iii@linux.ibm.com