Cell driver state-setter functions, basic tile get/put, glClear.

Cell driver state-setter functions, basic tile get/put, glClear.

The state setting code was mostly just copied from the softpipe driver.
The SPUs can now get/put framebuffer tiles from/to main memory and clear
them to a given color.  Lots of debug code in effect.
Tiled framebuffer is displayed in X window via the xmwinsys layer.
To enable Cell driver, export GALLIUM_CELL=1