drm/omap: check if rotation is supported before commit

omapdrm is missing a check on the validity of the rotation property.
This leads to omapdrm possibly trying to use rotation on non-rotateable
framebuffer, which causes the overlay setup to fail.

This patch adds the necessary check to omap_plane_atomic_check().

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