arm:dts:imx6: disable ldb in base device tree

The LDB is enabled via device tree overlay generated by gfxml2dto tool, depending on "display" settings in the XML configuration file.

There is a problem with HDMI output when "display" settings are missing in the XML configuration file.

The following errors can be observed in dmesg:

[    2.081476] /ldb/lvds-channel@0: could not find display-timings node
[    2.088014] /ldb/lvds-channel@0: no timings specified

It happens because gfxml2dto does not completely disable the "ldb" node, but disables only the "panel". After this, the DRM driver does not bind any device.

Issue-ID: 746-001527