OMAP: DSS: Minor cleanup in ovl and mgr cache structs

The overlay_cache_data and manager_cache_data structs include
the elements of omap_overlay_info and omap_overlay_manager_info
structs respectively. Include the structs instead of the individual
elements to reduce code.

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