[MIPS][microMIPS] Fix PseudoMTLOHI_MM matching and expansion
On micromips MipsMTLOHI is always matched to PseudoMTLOHI_DSP regardless
of +dsp argument. This patch checks is HasDSP predicate is present for
PseudoMTLOHI_DSP so PseudoMTLOHI_MM can be matched when appropriate.
Add expansion of PseudoMTLOHI_MM instruction into a mtlo/mthi pair.
Patch by Mirko Brkusanin.
Differential Revision: http://reviews.llvm.org/D59203