[mips] Implement eliminateCallFramePseudoInstr() in MipsFrameLowering. NFC.

Summary:
Avoid duplicate code in Mips16FrameLowering and MipsSEFrameLowering by
providing an implementation of the eliminateCallFramePseudoInstr()
function from their base class.

Depends on D8640.

Reviewers: dsanders

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8641

llvm-svn: 233909