Needed for kprobes support. Copied and adapted from arm64 code.

Guo Ren fixup pt_regs type for linux-5.8-rc1.
Signed-off-by: NPatrick Stählin <me@packi.ch>
Signed-off-by: NGuo Ren <guoren@linux.alibaba.com>
Reviewed-by: NPekka Enberg <penberg@kernel.org>
Reviewed-by: NZong Li <zong.li@sifive.com>
Reviewed-by: NMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: NPalmer Dabbelt <palmerdabbelt@google.com>