usb: cdns3: Add Cadence USB3 DRD Driver

This patch introduce new Cadence USBSS DRD driver to Linux kernel.

The Cadence USBSS DRD Controller is a highly configurable IP Core which
can be instantiated as Dual-Role Device (DRD), Peripheral Only and
Host Only (XHCI)configurations.

The current driver has been validated with FPGA platform. We have
support for PCIe bus, which is used on FPGA prototyping.

The host side of USBSS-DRD controller is compliant with XHCI
specification, so it works with standard XHCI Linux driver.

Signed-off-by: Pawel Laszczak <pawell@cadence.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/cdns3/gadget-export.h

@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Cadence USBSS DRD Driver - Gadget Export APIs.
+ *
+ * Copyright (C) 2017 NXP
+ * Copyright (C) 2017-2018 NXP
+ *
+ * Authors: Peter Chen <peter.chen@nxp.com>
+ */
+#ifndef __LINUX_CDNS3_GADGET_EXPORT
+#define __LINUX_CDNS3_GADGET_EXPORT
+
+#ifdef CONFIG_USB_CDNS3_GADGET
+
+int cdns3_gadget_init(struct cdns3 *cdns);
+void cdns3_gadget_exit(struct cdns3 *cdns);
+#else
+
+static inline int cdns3_gadget_init(struct cdns3 *cdns)
+{
+	return -ENXIO;
+}
+
+static inline void cdns3_gadget_exit(struct cdns3 *cdns) { }
+
+#endif
+
+#endif /* __LINUX_CDNS3_GADGET_EXPORT */