powerpc: Replace kretprobe code with rethook on powerpc

This is an adaptation of commit f3a112c0 ("x86,rethook,kprobes:
Replace kretprobe with rethook on x86") to powerpc.

Rethook follows the existing kretprobe implementation, but separates
it from kprobes so that it can be used by fprobe (ftrace-based
function entry/exit probes). As such, this patch also enables fprobe
to work on powerpc. The only other change compared to the existing
kretprobe implementation is doing the return address fixup in
arch_rethook_fixup_return().

Reference to other archs:
commit b57c2f12 ("riscv: add riscv rethook implementation")
commit 7b0a0964 ("LoongArch: Replace kretprobe with rethook")

Note:
=====

In future, rethook will be only for kretprobe, and kretprobe
will be replaced by fprobe.

https://lore.kernel.org/all/172000134410.63468.13742222887213469474.stgit@devnote2/



We will	adapt the above	implementation for powerpc once its upstream.
Until then, we can have	this implementation of rethook to serve
current	kretprobe usecases.

Reviewed-by: Naveen Rao <naveen@kernel.org>
Signed-off-by: Abhishek Dubey <adubey@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240830113131.7597-1-adubey@linux.ibm.com