usb: musb: only build musb_barebox if host is enabled
musb_barebox.c contains code that is only ever used if CONFIG_MUSB_HOST
is set. Building it uncoditionally breaks the build depending on the link
order.
Fixes:
drivers/usb/musb/musb_barebox.c:64: undefined reference to `musb_urb_enqueue'
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>