Want to stop passing x/y/width/height to Clear() function.

Want to stop passing x/y/width/height to Clear() function.
The coordinates need to be computed after we've got the hw lock.
Code updated to:
1. Ignore all/x/y/width/height/ params passed to Clear func.
2. Pass 0,0,0,0,0 to _swrast_Clear() until they're totally removed.