bpf: move kfunc_call_arg_meta higher in the file

Move struct bpf_kfunc_call_arg_meta higher in the file and put it next
to struct bpf_call_arg_meta, so it can be used from more functions.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230302235015.2044271-10-andrii@kernel.org


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