ARM: dts: colibri-imx6: Disable usb over-current

Disable usb over-current of the chipidea driver on all Carrier-Boards
used by Toradex. Do this as we don't want to use this functionality on
our Carrier Boards and to leave it open to someone who includes our
module-level device-trees.

Remove the now obsolete disable-over-current flag from module-level
device-tree imx6qdl-colibri.dtsi and leave it as already mentioned to
the people actually implementing the carrier-board to implement this.

This will prevent the warning "No over current polarity defined" from
being printed on boot.

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>