rockchip: defconfig: Increase max video resolution for mipi panel

The mipi panel used on evb-rk3399 has a 1920x1200 resolution. But now
the max resolution is 1920x1080. So increase it.

Signed-off-by: Eric Gao <eric.gao@rock-chips.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>