Fix a regression I introduced when I expanded the complex pseudos in

Fix a regression I introduced when I expanded the complex pseudos in
the Mips16 port. A few of the psuedos could either take signed
or unsigned arguments and I did not distinguish the case and improperly
rejected some valid cases that the assembler had previously accepted
when they were pure pseudos that expanded as assembly instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183633 91177308-0d34-0410-b5e6-96231b3b80d8