selftests/bpf: regroup and declare similar kfuncs selftests in an array

selftests/bpf: regroup and declare similar kfuncs selftests in an array

Similar to tools/testing/selftests/bpf/prog_tests/dynptr.c:
we declare an array of tests that we run one by one in a for loop.

Followup patches will add more similar-ish tests, so avoid a lot of copy
paste by grouping the declaration in an array.

For light skeletons, we have to rely on the offsetof() macro so we can
statically declare which program we are using.
In the libbpf case, we can rely on bpf_object__find_program_by_name().
So also change the Makefile to generate both light skeletons and normal
ones.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220906151303.2780789-2-benjamin.tissoires@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>