This patch handles unaligned loads and stores in Mips JIT. Mips backend

This patch handles unaligned loads and stores in Mips JIT. Mips backend
implements unaligned loads and stores with assembler macro-instructions
ulw, usw, ulh, ulhu, ush, and this patch emits corresponding instructions
instead of these macros. Since each unaligned load/store is expanded
into two corresponding loads/stores where offset for second load/store is
modified by +3 (for words) or +1 (for halfwords).

Patch by Petar Jovanovic and Sasa Stankovic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@144081 91177308-0d34-0410-b5e6-96231b3b80d8