selftests/bpf: Add kprobe multi write ctx attach test

selftests/bpf: Add kprobe multi write ctx attach test

Adding test to check we can't attach kprobe multi program
that writes to the context.

It's x86_64 specific test.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20250916215301.664963-7-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>