A number of small changes:
  - Change ConstantD for +/-zero constants to use the fp_zero register.
  - Use Bfi in DoConstructDouble.
  - Use Tbz for positive dividend check in mod by constant.
  - Optimize some deoptimize checks.
  - Fix a couple of style/consistency issues.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/272183003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21311 ce2b1a6d-e550-0410-aec6-3dcde31c8c00