usb: gadget: fsl: fix link error against usb-gadget module

The dependency to ensure this driver links correctly fails since
it can not be a loadable module:

drivers/usb/phy/phy-fsl-usb.o: In function `fsl_otg_set_peripheral':
phy-fsl-usb.c:(.text+0x2224): undefined reference to `usb_gadget_vbus_disconnect'

Make the option 'tristate' so it can work correctly.

Fixes: 5a8d651a ("usb: gadget: move gadget API functions to udc-core")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/phy/Kconfig

@@ -21,7 +21,7 @@ config AB8500_USB
 	  in host mode, low speed.
 
 config FSL_USB2_OTG
-	bool "Freescale USB OTG Transceiver Driver"
+	tristate "Freescale USB OTG Transceiver Driver"
 	depends on USB_EHCI_FSL && USB_FSL_USB2 && USB_OTG_FSM=y && PM
 	depends on USB_GADGET || !USB_GADGET # if USB_GADGET=m, this can't be 'y'
 	select USB_PHY