drm: omapdrm: Switch crtc and plane set_property to atomic helpers

Allow setting up plane properties atomically using the plane
set_property atomic helper. The properties are now stored in the plane
state (requiring subclassing it) and applied when updating the planes.

The CRTC exposes the properties of its primary plane for legacy reason.
We can't get rid of that API, so simply delegate it to the primary
plane.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>