If the divisor is a Power-of-2 constant, we could use shifts instead of the
expensive idiv instructions, which also loose the register constraints.

Review URL: https://chromiumcodereview.appspot.com/11478043
Patch from Yuqiang Xian <yuqiang.xian@intel.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13178 ce2b1a6d-e550-0410-aec6-3dcde31c8c00