OMAPDSS: move ovl & ovl-mgr init to apply.c

Overlay and overlay_manager structs will only be needed in the compat
mode.

This patch moves initialization of overlay and overlay_manager structs
to apply.c, so that they are handled in omapdss_compat_init().

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