drm/gma500: Move to private save/restore hooks

drm/gma500: Move to private save/restore hooks

I want to remove the core ones since with atomic drivers system
suspend/resume is solved much differently. And there's only 2 drivers
(nouveau besides gma500) really using them.

v2: Fixup build noise 0day reported.

Cc: Patrik Jakobsson <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
Reviewed-by: Thierry Reding <[email protected]> (v1)