ARM64: Faster immediate check and fix corner cases

Improve the code used to check for encodable logical immediates, fix some corner
cases associated with moving kWMinInt into W registers, and add tests.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/341123003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22120 ce2b1a6d-e550-0410-aec6-3dcde31c8c00