[mips][microMIPS] Delay slot filler: Replace the microMIPS JR with the JRC

[mips][microMIPS] Delay slot filler: Replace the microMIPS JR with the JRC

This patch adds functionality in MIPS delay slot filler such as if delay slot
filler have to put NOP instruction into the delay slot of microMIPS JR
instruction, then instead of emitting NOP this instruction is replaced by
compact jump instruction JRC.

Differential Revision: http://reviews.llvm.org/D7522

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229128 91177308-0d34-0410-b5e6-96231b3b80d8