usb: dwc3: remove extcon dependency

It is required by the OMAP glue driver, but it already depends
on it. The core driver should not depend on it. This will
allow the use of the PCI glue driver again.
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/Kconfig

 config USB_DWC3
 	tristate "DesignWare USB3 DRD Core Support"
 	depends on (USB || USB_GADGET) && HAS_DMA
-	depends on EXTCON
 	select USB_XHCI_PLATFORM if USB_SUPPORT && USB_XHCI_HCD
 	help
 	  Say Y or M here if your system has a Dual Role SuperSpeed