[mips][ias] Range check uimm2 operands and fix a bug this revealed.

Summary:
The bug was that the MIPS32R6/MIPS64R6/microMIPS32R6 versions of LSA and DLSA
(unlike the MSA version) failed to account for the off-by-one encoding of the
immediate. The range is actually 1..4 rather than 0..3.

Reviewers: vkalintiris

Subscribers: atanasyan, dsanders, llvm-commits

Differential Revision: http://reviews.llvm.org/D14015

llvm-svn: 252295