ARM: dts: imx6dl: prtrvt, prtvt7, prti6q, prtwd2: fix USB related warnings

Fix USB-related warnings in prtrvt, prtvt7, prti6q and prtwd2 device trees
by disabling unused usbphynop1 and usbphynop2 USB PHYs and providing proper
configuration for the over-current detection. This fixes the following
warnings with the current kernel:
 usb_phy_generic usbphynop1: dummy supplies not allowed for exclusive requests
 usb_phy_generic usbphynop2: dummy supplies not allowed for exclusive requests
 imx_usb 2184200.usb: No over current polarity defined

By the way, fix over-current detection on usbotg port for prtvt7, prti6q
and prtwd2 boards. Only prtrvt do not have OC on USB OTG port.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>