drm/gma500: Fix hibernation problems on sdvo encoders

The state of the SDVO chip is more difficult to save than the LVDS so we do a
full mode set on the crtc to get SDVO operational again. The SDVOB/C register is
also stored just in case we have special bits set in the future.

Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>