[mips] Use TwoOperandAliasConstraint for shift instructions.

This enables TableGen to generate an additional two operand
matcher for our shift_rotate_imm and shift_rotate_reg class of instructions.

The tests were also updated so that they include now encoding information
for all affected instructions.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206398 91177308-0d34-0410-b5e6-96231b3b80d8