[arm] Fix UBFX detection.
[arm] Fix UBFX detection.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/725063002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#25344}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh