Initial add of i2s_loopback test

tests/i2s_loopback/usb_device.xc

@@ -0,0 +1,32 @@
+#if 0
+// Copyright (c) 2016, XMOS Ltd, All rights reserved
+#include <xs1.h>
+#include <xccompat.h>
+#include "usb_std_requests.h"
+#include "xud.h"
+#include "usb_device.h"
+
+unsigned char g_currentConfig = 0;
+unsigned char g_interfaceAlt[16];
+
+XUD_Result_t USB_GetSetupPacket(XUD_ep ep_out, XUD_ep ep_in, REFERENCE_PARAM(USB_SetupPacket_t, sp))
+{
+  return XUD_RES_OKAY;
+}
+
+XUD_Result_t USB_StandardRequests(XUD_ep ep_out, XUD_ep ep_in,
+    NULLABLE_ARRAY_OF(unsigned char, devDesc_hs), int devDescLength_hs,
+    NULLABLE_ARRAY_OF(unsigned char, cfgDesc_hs), int cfgDescLength_hs,
+    NULLABLE_ARRAY_OF(unsigned char, devDesc_fs), int devDescLength_fs,
+    NULLABLE_ARRAY_OF(unsigned char, cfgDesc_fs), int cfgDescLength_fs,
+#ifdef __XC__
+    char * unsafe strDescs[],
+#else
+    char * strDescs[],
+#endif
+    int strDescsLength, REFERENCE_PARAM(USB_SetupPacket_t, sp), XUD_BusSpeed_t usbBusSpeed)
+{
+  return XUD_RES_OKAY;
+}
+
+#endif