[arm] Recognize comparisons of shifts with zero.

For example, recognize

  0 == r1 << r2

and generate a single

  MOVS rt, r1, lsl r2

instruction.

TEST=cctest,compiler-unittests
R=jarin@chromium.org

Review URL: https://codereview.chromium.org/478233002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23148 ce2b1a6d-e550-0410-aec6-3dcde31c8c00