Instead of restoring registers blindly, restart the LCDC by going
through the startup sequence when resuming from runtime PM suspend. All
registers are now correctly initialized in the right order.

As a side effect, this also gets rid fo a possible panning restore issue
caused by always saving the frame buffer base address registers from set
A instead of the currently active set.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>