MIPS: CPS: Fix r1 .set mt assembler warning

MIPS: CPS: Fix r1 .set mt assembler warning

MIPS CPS has a build warning on kernels configured for MIPS32R1 or
MIPS64R1, due to the use of .set mt without a prior .set mips{32,64}r2:

arch/mips/kernel/cps-vec.S Assembler messages:
arch/mips/kernel/cps-vec.S:238: Warning: the `mt' extension requires MIPS32 revision 2 or greater

Add .set MIPS_ISA_LEVEL_RAW before .set mt to silence the warning.

Fixes: 245a7868d2f2 ("MIPS: smp-cps: rework core/VPE initialisation")
Signed-off-by: James Hogan <jhogan@kernel.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: James Hogan <james.hogan@mips.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17699/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>