usb: musb: Fix compilation of gadget code

usb: musb: Fix compilation of gadget code

musb udc code depends on usb gadget code provided by CONFIG_USB_DEVICE as
defined in drivers/usb/gadget/Makefile. But this Makefile is not included
into U-Boot build when CONFIG_USB_GADGET is not set. As CONFIG_USB_DEVICE
cannot be enabled together with CONFIG_USB_GADGET it means that dependency
for musb udc code is not compiled during build. Fix it by including
drivers/usb/gadget dependency also when CONFIG_USB_DEVICE is set.

This patch fixes compile errors:

arm-linux-gnueabi-ld.bfd: drivers/usb/musb/built-in.o: in function `musb_peri_ep0_rx':
u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `ep0_recv_setup'
arm-linux-gnueabi-ld.bfd: drivers/usb/musb/built-in.o: in function `musb_peri_ep0_idle':
u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `ep0_recv_setup'
arm-linux-gnueabi-ld.bfd: drivers/usb/musb/built-in.o: in function `musb_peri_ep0_zero_data_request':
u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_device_event_irq'
arm-linux-gnueabi-ld.bfd: drivers/usb/musb/built-in.o: in function `musb_peri_ep0_idle':
u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `ep0_recv_setup'
arm-linux-gnueabi-ld.bfd: drivers/usb/musb/built-in.o: in function `musb_peri_ep0_rx':
u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_rcv_complete'
arm-linux-gnueabi-ld.bfd: drivers/usb/musb/built-in.o: in function `musb_peri_rx_ep':
u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_rcv_complete'
arm-linux-gnueabi-ld.bfd: drivers/usb/musb/built-in.o: in function `udc_endpoint_write':
u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_tx_complete'
arm-linux-gnueabi-ld.bfd: drivers/usb/musb/built-in.o: in function `udc_irq':
u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_device_event_irq'
arm-linux-gnueabi-ld.bfd: u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_device_event_irq'
arm-linux-gnueabi-ld.bfd: u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_device_event_irq'
arm-linux-gnueabi-ld.bfd: u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_device_event_irq'
arm-linux-gnueabi-ld.bfd: u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_device_event_irq'
arm-linux-gnueabi-ld.bfd: drivers/usb/musb/built-in.o:u-boot/drivers/usb/musb/musb_udc.c: more undefined references to `usbd_device_event_irq' follow
arm-linux-gnueabi-ld.bfd: drivers/usb/musb/built-in.o: in function `udc_setup_ep':
u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_alloc_urb'
arm-linux-gnueabi-ld.bfd: drivers/usb/musb/built-in.o: in function `udc_startup_events':
u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_device_event_irq'
arm-linux-gnueabi-ld.bfd: u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_device_event_irq'
arm-linux-gnueabi-ld.bfd: u-boot/drivers/usb/musb/musb_udc.c: undefined reference to `usbd_device_event_irq'
make: *** [Makefile:1762: u-boot] Error 1

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Acked-by: Pavel Machek <pavel@ucw.cz>