[mips] Teach the delay slot filler to transform 'jal' for microMIPS

ISel is currently picking 'JAL' over 'JAL_MM' for calling a function when
targeting microMIPS. A later patch will correct this behaviour.

This patch extends the mechanism for transforming instructions into their short
delay to recognise 'JAL_MM' for transforming into 'JALS_MM'.

llvm-svn: 330825