mac68k: start CUDA early

The valkyriefb driver needs the CUDA to work in order to set the video
mode at boot. So initialise the device earlier, and bring the m68k code
closer to the powermac code.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>