This function allows upper layer to check if a requested atomic update
to the plane has been applied or is still pending.
Signed-off-by: NLucas Stach <l.stach@pengutronix.de>
[p.zabel@pengutronix.de: inverted logic: done -> pending]
Signed-off-by: NPhilipp Zabel <p.zabel@pengutronix.de>