mips: Save all registers when saving the frame

mips: Save all registers when saving the frame

The MIPS frame save code was just saving a few registers, enough to
do a backtrace if every function set up a frame.  However, this is
not working if you are using DWARF unwinding, because most of the
registers are wrong.  This was causing kdump backtraces to be short
or bogus.

So save all the registers.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16989/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>