usb: move CONFIG_USB_XHCI_DWC3 to Kconfig

Create an entry for "config USB_XHCI_DWC3" in Kconfig and
switch over to it for all boards.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/drivers/usb/host/Kconfig b/drivers/usb/host/Kconfig
index 8a6f732..89580cc 100644
--- a/drivers/usb/host/Kconfig
+++ b/drivers/usb/host/Kconfig
@@ -18,6 +18,12 @@
 	---help---
 	  Enables support for the on-chip xHCI controller on UniPhier SoCs.
 
+config USB_XHCI_DWC3
+	bool "DesignWare USB3 DRD Core Support"
+	help
+	  Say Y or if your system has a Dual Role SuperSpeed
+	  USB controller based on the DesignWare USB3 IP Core.
+
 endif
 
 config USB_OHCI_GENERIC