Since ulpi bus driver is located at usb/common/ulpi.c, whether it
is compiled or not depends on CONFIG_USB_COMMON which needs either
USB Host or USB Gadget is enabled, so even CONFIG_USB_ULPI_BUS is
chosen, its source may still not be compiled when both USB HOST
and USB gadget are disabled.

It fixed compile error with below configurations:
- # CONFIG_USB is not set
- # CONFIG_USB_GADGET is not set
- CONFIG_PHY_TUSB1210=m
- CONFIG_USB_ULPI_BUS=m

>> All errors (new ones prefixed by >>):
>>
>> ERROR: "ulpi_unregister_driver" [drivers/phy/phy-tusb1210.ko] undefined!
>> ERROR: "__ulpi_register_driver" [drivers/phy/phy-tusb1210.ko] undefined!
>> ERROR: "ulpi_write" [drivers/phy/phy-tusb1210.ko] undefined!

Fixes: ad764c49

 ("usb: Kconfig: move ulpi bus support out of host")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>