The previous register allocation allowed invalid register aliasing in
cases where in the TF graph the node was used for multiple inputs of the
Word32PairShl node.

Additionally I renamed PairLsl to LslPair in the code generation for
consistency.

R=titzer@chromium.org, v8-arm-ports@googlegroups.com

Review URL: https://codereview.chromium.org/1776393004

Cr-Commit-Position: refs/heads/master@{#34755}