[Constant Hoisting][ARM64] Enable constant hoisting for ARM64.

This implements the target-hooks for ARM64 to enable constant hoisting.

This fixes <rdar://problem/14774662> and <rdar://problem/16381500>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205791 91177308-0d34-0410-b5e6-96231b3b80d8