[AArch64] Simplify callee-save register save/restore. NFC.
Summary:
Simplify callee-save register save/restore code generation by
remembering the size of the callee-save area when it is computed so we
don't have to scan the prologue/epilogue instructions again later to
reconstruct it.
This is intended to simplify follow-on changes that reduce the number of
registers saved/restored.
Reviewers: mcrosier, jmolloy, t.p.northover
Subscribers: aemerson, rengolin, mcrosier, llvm-commits
Differential Revision: http://reviews.llvm.org/D16732
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@259365
91177308-0d34-0410-b5e6-
96231b3b80d8