staging: drm/imx: Fix YUYV support in i.MX IPUv3 base driver

YVYU is not supported by the IPU, so remove partial handling
of this format and replace it with YUYV which is supported.

Signed-off-by: Michael Olbrich <m.olbrich@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>