Merge branch 'selftests-bpf-fix-a-few-issues-in-arena_spin_lock'

Merge branch 'selftests-bpf-fix-a-few-issues-in-arena_spin_lock'

Ilya Leoshkevich says:

====================
I tried running the arena_spin_lock test on s390x and ran into the
following issues:

* Changing the header file does not lead to rebuilding the test.
* The checked for number of CPUs and the actually required number of
  CPUs are different.
* Endianness issue in spinlock definition.

This series fixes all three.
====================

Link: https://patch.msgid.link/20250424165525.154403-1-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>