OMAPDSS: OMAPFB: always allow to configure overlay

Currently when multiple overlays are active, OMAPFB_SETUP_PLANE fails.
Instead of failing, allow it to configure the first overlay as if there
was only one overlay, the remaining ones will have to be configured in
other ways (sysfs).

This allows overlay-controlling programs (like video players) to function
properly when framebuffer is cloned to another display (like TV).

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>