drm, gma500: Fix Cedarview boot failures in 3.3-rc

Production GMA3600/3650 hardware turns out to be subtly different to the
development platforms.  This combined with a minor driver bug is causing
the kernel to hang on these platforms.

This patch does the following

 - turn down a couple of messages that were meant to be debug and are
   causing much confusion

 - ensure the hotplug interrupt is disabled on Cedartrail systems.

 - fix a bug where gtt roll mode called psbfb_sync, which tries to sync
   the 2D engine. On other devices it is harmless as the 2D engine is
   present but not in use when in gtt roll mode, on Cedartrail it causes
   a hang

Without these changes 3.3-rc hangs on boot on Cedartrail based systems.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>