dm: video: Add a video uclass

dm: video: Add a video uclass

U-Boot has separate code for LCDs and 'video' devices. Both now use a
very similar API thanks to earlier work by Nikita Kiryanov. With the driver-
model conversion we should unify these into a single uclass.

Unfortunately there are different features supported by each. This
implementation provides for a common set of features which should serve
most purposes. The intent is to support:

- bitmap devices with 8, 16 and 32 bits per pixel
- text console wih white on black or vice versa
- rotated text console
- bitmap display (BMP format)

More can be added as additional boards are ported over to use driver model
for video.

The name 'video' is chosen for the uclass since it is more generic than LCD.
Another option would be 'display' but that would introduce a third concept
to U-Boot which seems like the wrong approach.

The existing LCD and video init functions are not needed now, so this uclass
makes no attempt to implement them.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Anatolij Gustschin <agust@denx.de>