[Mips Assembler] Add support for OR macro with imediate opperand

Mips assembler supports macros that allows the OR instruction 
to have an immediate parameter. This patch adds an instruction 
alias that converts this macro into a Mips ORI instruction. 

Contributer: Vladimir Medic


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178316 91177308-0d34-0410-b5e6-96231b3b80d8