x86: edison: Use dwc3-generic driver for Intel Edison

Use generic Synopsys DesignWare 3 driver on Intel Edison.
For now it's just a stub which allows future refactoring.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/x86/dts/edison.dts

@@ -105,6 +105,10 @@
 		reg = <0xff009000 0x1000>;
 	};
 
+	usb: usb@f9100000 {
+		compatible = "intel,tangier-dwc3";
+	};
+
 	watchdog: wdt@0 {
 		compatible = "intel,tangier-wdt";
 	};