Define the full 1024M of ram on the imx53 QSB board.
Fix the ATI backlight driver off/on handling.  Now this driver works correctly
with the ATI Radeon 9700 in the PowerBook G4 1.67GHz.

Code shamelessly taken in spirit from the radeonkms driver, which I hope will
make this driver redundant in the future.

MFC after:	2 weeks