usb: bdc: Enable in Kconfig for ARCH_BRCMSTB systems

Many ARM based Broadcom STB SoC's have a USB BDC controller so
enable this driver for these systems.
Signed-off-by: Al Cooper <alcooperx@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/bdc/Kconfig

 config USB_BDC_UDC
 	tristate "Broadcom USB3.0 device controller IP driver(BDC)"
 	depends on USB_GADGET && HAS_DMA
+	default ARCH_BRCMSTB
 
 	help
 	BDC is Broadcom's USB3.0 device controller IP. If your SOC has a BDC IP