MIPS: Move register dump routines out of ptrace code

MIPS: Move register dump routines out of ptrace code

Current register dump methods for MIPS are implemented inside ptrace
methods, but there will be other uses in the kernel for them, so keep
them separately in process.c and use those definitions for ptrace
instead.

Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14587/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>