[PATCH v2] riscv: Fix RV32 libthread_db THREAD_SELF register layout

[Shengwen Cheng]

Hi Peter,

I do not have push access, and I do not have a GNU copyright assignment
on file.  I would like to submit this under DCO.

Let me send a v3 with my Signed-off-by and your Reviewed-by added.
Could you help push it after that?

Thanks,
Shengwen