fprobe: Add entry/exit callbacks types

We are going to store callbacks in following change,
so this will ease up the code.

Link: https://lore.kernel.org/all/20240207153550.856536-2-jolsa@kernel.org/



Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>