[AArch64] Enable SeparateConstOffsetFromGEP, EarlyCSE and LICM passes on AArch64 backend.
SeparateConstOffsetFromGEP can gives more optimizaiton opportunities related to GEPs, which benefits EarlyCSE
and LICM. By enabling these passes we can have better address calculations and generate a better addressing
mode. Some SPEC 2006 benchmarks (astar, gobmk, namd) have obvious improvements on Cortex-A57.

Reviewed in http://reviews.llvm.org/D5864.