gpu: ipu-v3: Use videomode in struct ipu_di_signal_cfg

This patch changes struct ipu_di_signal_cfg to use struct videomode
to define video timings and flags.

Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>