MIPS: Fix MSA asm warnings in control reg accessors

Building an MSA capable kernel with a toolchain that supports MSA
produces warnings such as this:

  CC      arch/mips/kernel/cpu-probe.o
{standard input}: Assembler messages:
{standard input}:4786: Warning: the `msa' extension requires 64-bit FPRs

This is due to ".set msa" without ".set fp=64" in the inline assembly of
control register accessors, since MSA requires the 64-bit FPU registers
(FR=1). Add the missing fp=64 in these functions to silence the
warnings.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13554/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>