ARM: fix assertions for uxtb and co.

Allow operands with ROR #0. Behind the scene they are mapped to LSL #0.

BUG=v8:3209
LOG=N
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/198053014

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20171 ce2b1a6d-e550-0410-aec6-3dcde31c8c00