dm: video: Repurpose the 'displayport' uclass to 'display'

dm: video: Repurpose the 'displayport' uclass to 'display'

The current DisplayPort uclass is too specific. The operations it provides
are shared with other types of output devices, such as HDMI and LVDS LCD
displays.

Generalise the uclass so that it can be used with these devices as well.
Adjust the uclass to handle the EDID reading and conversion to
display_timing internally.

Also update nyan-big which is affected by this.

Signed-off-by: Simon Glass <sjg@chromium.org>