[turbofan] Avoid useless bit masking in typed lowering.

There's no need to apply the 0x1f mask to right hand sides of shifts if
the input is already in range [0,31].

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

Review URL: https://codereview.chromium.org/718193003

Cr-Commit-Position: refs/heads/master@{#25313}