Finish getting Mips fast-isel to match up with AArch64 fast-isel

Summary:
In order to facilitate use of common code, checking by reviewers of other fast-isel ports, and hopefully to eventually move most of Mips and other fast-isel ports into target independent code, I've tried to get the two implementations to line up.

There is no functional code change. Just methods moved in the file to be in the same order as in AArch64.

Test Plan: No functional change.

Reviewers: dsanders

Reviewed By: dsanders

Subscribers: llvm-commits, aemerson, rfuhler

Differential Revision: http://reviews.llvm.org/D5692

llvm-svn: 219703