[Aarch64] Add pass LoopDataPrefetch for Cyclone

Summary:
This wires up the pass for Cyclone but keeps it off for now because we
need a few more TTIs.

The getPrefetchMinStride value is not very well tuned right now but it
works well with CFP2006/433.milc which motivated this.

Tests will be added as part of the upcoming large-stride prefetching
patch.

Reviewers: t.p.northover

Subscribers: llvm-commits, aemerson, hfinkel, rengolin

Differential Revision: http://reviews.llvm.org/D17943

llvm-svn: 263770