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/364653003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22148 ce2b1a6d-e550-0410-aec6-3dcde31c8c00