OMAP: DSS2: Fix update area calculations with multiple scaled overlays

When there are multiple scaled overlays simply checking whether the update
area intersects any of them in order is not enough. If eg. VID1 starts out
completely outside the update area but VID2 causes the update area to
increase in such a way that VID1 now falls partially within the increased
update area VID1 should be rechecked and the update area possibly
increased even further to fully encompass VID1. So simply keep looping
over the overlays until such time that none of the overlays caused the
update area to change.

Signed-off-by: Ville Syrjälä <ville.syrjala@nokia.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>