[mips][micrompis] Emit 16bit NOPs by default

Emit 16bit NOPs by default.
Use 32bit NOPs in delay slots where necessary.

Differential https://reviews.llvm.org/D55323



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350733 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed