usb: dwc3: select USB_ROLE_SWITCH

Calling into the role switch API requires that these functions
are loaded, if they are in a loadable module and dwc3 itself
is built-in, this produces a link error:

drivers/usb/dwc3/drd.o: In function `dwc3_usb_role_switch_get':
drd.c:(.text+0x26): undefined reference to `usb_role_switch_get_drvdata'
drivers/usb/dwc3/drd.o: In function `dwc3_usb_role_switch_set':
drd.c:(.text+0x97): undefined reference to `usb_role_switch_get_drvdata'
drivers/usb/dwc3/drd.o: In function `dwc3_drd_init':
drd.c:(.text+0x1ca7): undefined reference to `usb_role_switch_register'
drivers/usb/dwc3/drd.o: In function `dwc3_drd_exit':
drd.c:(.text+0x1e92): undefined reference to `usb_role_switch_unregister'

Select the USB_ROLE_SWITCH symbol from dwc3 in that configuration.

Fixes: 0339f7fb ("usb: dwc3: fix up for role switch API change")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Felipe Balbi <balbi@kernel.org>