backends: Add frame pointer unwinding for LoongArch

backends: Add frame pointer unwinding for LoongArch

If we don't find any debug information for a given frame, we usually
cannot unwind any further. However, the binary in question might have
been compiled with frame pointers, in which case we can look up the
well known frame pointer locations in the stack snapshot and use them
to bridge the frames without debug information.

Signed-off-by: Liwei Ge <geliwei@openanolis.org>
Signed-off-by: Youling Tang <tangyouling@loongson.cn>