video: rockchip: Support 4K resolution for rk3399, HDMI

The default resolution for rockchip display is 1920x1080
which failed to work on 4K HDMI out displays on rk3399.

So, mark the default resolution as 3480x2160 for rk3399
HDMI out.

This would work all the hdmi display resolutions till
4K.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Tested-by: Peter Robinson <pbrobinson@gmail.com>