MIPS: asm/reg.h: Move to uapi

This header defines an exported interface (the register layout used in
core dumps and the GP regset accessible with PTRACE_{GET,SET}REGSET),
therefore belongs in uapi.

Signed-off-by: Alex Smith <alex@alex-smith.me.uk>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7458/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>