usb: dwc2: disable erroneous overcurrent condition

For the case where an external VBUS is used, we should enable the external
VBUS comparator in the driver. This would prevent an unnecessary
overcurrent error which would then disable the host port.

This patch uses the standard 'disable-over-current' binding to allow of the
option of disabling the over-current condition.

Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>