[mips] Splitting up class definition from implementation.

Also removed some unnecessary #includes.

No functional changes.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204320 91177308-0d34-0410-b5e6-96231b3b80d8
Mark alias symbols as microMIPS if necessary.   Differential Revision: http://llvm-reviews.chandlerc.com/D3080

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204323 91177308-0d34-0410-b5e6-96231b3b80d8