gma500: begin the config based split

We don't want to carry all the extra gunk around on every device so use the
splitting work so far to tidy this up. Poulsbo is still mandatory as it is
used in bits by the other drivers and not neatly modularised.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>