sunxi: video: add LCD support to DE2 driver

Extend DE2 driver with LCD support. Tested on Pinebook which is based
on A64 and has ANX6345 eDP bridge with eDP panel connected to it.

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
[agust: rebased v5 on u-boot-video/master]
Signed-off-by: Anatolij Gustschin <agust@denx.de>