[mips][ias] Move createCpRestoreMemOp to MipsTargetStreamer. NFC.

Summary:
This removes the temporary call to isIntegratedAssemblerRequired() which was
added recently. It's effect is now acheived directly in the MipsTargetStreamer
hierarchy.

Reviewers: sdardis

Subscribers: dsanders, sdardis, llvm-commits

Differential Revision: http://reviews.llvm.org/D19715

llvm-svn: 268058