rockchip: Drop call to rockchip_dnl_mode_check() for now

This function causes a 5-second delay and stops the display working on
minnie. This code should be in a driver and should only be enabled by
a device-tree property, so that it does not affect devices which do not
have this feature.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>