OMAPDSS: APPLY: add wait_pending_extra_info_updates()

Add wait_pending_extra_info_updates() function which can be used to wait
until any extra_info changes have been taken into use by the hardware.
This can be only called when holding the apply mutex, so that other
threads cannot insert new extra_info changes.

This will be used to handle fifo-configurations.

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