[Mips] Add instruction selection for strict FP (#168870)
This consists of marking the various strict opcodes as legal, and
adjusting instruction selection patterns so that 'op' is 'any_op'. The
changes are similar to those in D114946 for AArch64 and #160696 for ARM.
Only Mips32/64 FPU instructions are affected.
Added lowering for for STRICT_FP_TO_UINT and STRICT_FP_TO_SINT ops.
