ps3fb/vram: Extract common GPU stuff into <asm/ps3gpu.h>

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Cc: linux-fbdev-devel@lists.sourceforge.net
Cc: Jim Paris <jim@jtan.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>