selftests/bpf: Add global subprog context passing tests

Add tests validating that it's possible to pass context arguments into
global subprogs for various types of programs, including a particularly
tricky KPROBE programs (which cover kprobes, uprobes, USDTs, a vast and
important class of programs).

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20230216045954.3002473-4-andrii@kernel.org