[mips] Handle the emission of microMIPSr6 sll instruction when used as a nop.

This instruction is encoded as zero, so we have handle that case when checking
for unimplemented opcodes when producing the encoding for an instruction.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321066 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed