uboot-imx

x86: Adjust config to support DM_VIDEO

Update the common configuration so that it works correctly when
CONFIG_DM_VIDEO is enabled. This involves dropping the legacy CONFIG_VIDEO
option and changing the stdio device from "vga" to "vidconsole".

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>