dm: video: Implement the bmp command for driver model

This command can use the bitmap display code in the uclass. This is similar
to the code in lcd.c and cfb_console.c. These other copies will go away when
all boards are converted to use driver model for video.

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