AArch64: Use TTI branch functions in branch relaxation

The main change is to return the code size from
InsertBranch/RemoveBranch.

Patch mostly by Tim Northover

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@281505 91177308-0d34-0410-b5e6-96231b3b80d8
36 files changed