drm/armada: remove crtc YUV colourspace properties

Remove the unused CRTC colourspace properties - userspace does not make
use of these.  In any case, these are not a property of the CRTC, since
they demonstrably only affect the video (overlay) plane, irrespective
of the format of the graphics (primary) plane.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>