selftests/bpf: Add tests for arena spin lock

Add some basic selftests for qspinlock built over BPF arena using
cond_break_label macro.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250306035431.2186189-4-memxor@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>