arch: riscv: implement frame-pointer based stack unwinding

Influenced heavily by the RISCV64 stack unwinding
implementation in the Linux kernel.

`CONFIG_RISCV_EXCEPTION_STACK_TRACE` can be enabled by
configuring the following Kconfigs:

```prj.conf
CONFIG_DEBUG_INFO=y
CONFIG_EXCEPTION_STACK_TRACE=y
CONFIG_OVERRIDE_FRAME_POINTER_DEFAULT=y
CONFIG_OMIT_FRAME_POINTER=n
```

Signed-off-by: Yong Cong Sin <ycsin@meta.com>