SDAG: Implement Select instead of SelectImpl in AArch64DAGToDAGISel
This one has a lot of code churn, but it's all mechanical and
straightforward.
- Where we were returning a node before, call ReplaceNode instead.
- Where we would return null to fall back to another selector, rename
the method to try* and return a bool for success.
- Where we were calling SelectNodeTo, just return afterwards.
Part of llvm.org/pr26808.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@269379
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