X87: Move register conventions out of the IC classes.

port r23391.

original commit message:
  Move register conventions out of the IC classes.
  A change to a convention shouldn't require recompilation of ic.h/.cc.

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/513533003

Patch from Chunyang Dai <chunyang.dai@intel.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23428 ce2b1a6d-e550-0410-aec6-3dcde31c8c00