staging: drm/imx: ipu-dc: add 24-bit GBR support to DC

24-bit GBR order is needed on the display interface connected
to the Television Encoder (TVEv2) on i.MX53.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>