[mips] Use uimm5 and uimm6 instead of shamt and imm, if the immediate has to fit
into a 5-bit or 6-bit field.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190226 91177308-0d34-0410-b5e6-96231b3b80d8