[mips][msa] Remove range checks for non-immediate sld.[bhwd] instructions

Removes immediate range checks for these instructions, since they have GPR
rt as their input operand.

Patch by Stefan Maksimovic.

Differential Revision: https://reviews.llvm.org/D30693


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@297485 91177308-0d34-0410-b5e6-96231b3b80d8