selftests/bpf: Check combination of jit blinding and pointers to bpf subprogs.

Check that ld_imm64 with src_reg=1 (aka BPF_PSEUDO_FUNC) works
with jit_blinding.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220513011025.13344-2-alexei.starovoitov@gmail.com