[ARM] Add macro fusion for AES instructions.

Summary:
This patch adds a macro fusion using CodeGen/MacroFusion.cpp to pair AES
instructions back to back and adds FeatureFuseAES to enable the feature.

Reviewers: evandro, javed.absar, rengolin, t.p.northover

Reviewed By: javed.absar

Subscribers: aemerson, mgorny, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D34142

llvm-svn: 305988