samples/kprobes: Add riscv support

Add riscv specific info dump in both handler_pre() and handler_post().

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>