OMAPDSS: APPLY: add checking of ovls/mgrs settings

Add checks for overlay and manager settings. The checks are a bit
complex, as we need to observe the bigger picture instead of overlays
and managers independently. Things like the used display and the zorder
of other overlays affect the validity of the settings.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>