Add USB Audio 1.0 support

Original commit credit to Amaury Pouly, Moshe Piekarski
Pushed across the finish line by Dana Conrad

To enable, see setting under General Settings --> System --> USB-DAC.
On devices with few endpoints, this may not work while HID and/or
mass storage is enabled.

Adds new dedicated mixer channel.

setting usb-dac can have values:
- never (0)
- always (1)
- while_charge_only (2)
- while_mass_storage (3)

Relevant devices are DWC2 and ARC usb controller devices. That being:
x1000 Native targets (m3k, erosqnative, q1, others...?),
sansac200, creativezenxfi2, vibe500, ipodmini2g,
ipod4g, creativezenxfi, creativezenxfi3, sansaview, ipodcolor,
creativezenxfistyle, samsungypz5, sansafuzeplus, iriverh10_5gb,
tatungtpj1022, gigabeats, faketarget, samsungyh820, gogearhdd1630, samsungyh925, ipodmini1g, ipodvideo, creativezenmozaic, sonynwze370, creativezen, gogearsa9200, gogearhdd6330, sonynwze360, sansae200, mrobe100, iriverh10, creativezenv, ipodnano1g, samsungyh920

USB Driver-wise, it should be noted that this patch requires some
slight changes:
- proper blocking on control OUT transfers, to make sure the data is
  received *before* using it, the usb_core should probably use that too
- drivers can now support interface alternate settings
- drivers can be notified of completion by a new fast handler, which
  is called directly from the driver; this is is necessary for
  isochronous transfers because going through the usb queue is way too
  slow

Designware changes:

- enable for USBOTG_DESIGNWARE
- set maxpacketsize to 1023 for ISO endpoints

Change-Id: I570871884a4e4820b4312b203b07701f06ecacc6

firmware/export/usb_drv.h

@@ -74,6 +74,7 @@ void usb_drv_stall(int endpoint, bool stall,bool in);
 bool usb_drv_stalled(int endpoint,bool in);
 int usb_drv_send(int endpoint, void* ptr, int length);
 int usb_drv_send_nonblocking(int endpoint, void* ptr, int length);
+int usb_drv_recv_blocking(int endpoint, void* ptr, int length);
 int usb_drv_recv_nonblocking(int endpoint, void* ptr, int length);
 void usb_drv_control_response(enum usb_control_response resp,
                               void* data, int length);
@@ -86,6 +87,14 @@ void usb_drv_set_test_mode(int mode);
 bool usb_drv_connected(void);
 int usb_drv_request_endpoint(int type, int dir);
 void usb_drv_release_endpoint(int ep);
+#ifdef USB_HAS_ISOCHRONOUS
+/* returns the last received frame number (the 11-bit number contained in the last SOF):
+ * - full-speed: the host sends one SOF every 1ms (so 1000 SOF/s)
+ * - high-speed: the hosts sends one SOF every 125us but each consecutive 8 SOF have the same frame
+ *   number
+ * thus in all mode, the frame number can be interpreted as the current millisecond *in USB time*. */
+int usb_drv_get_frame_number(void);
+#endif
 
 /* USB_STRING_INITIALIZER(u"Example String") */
 #define USB_STRING_INITIALIZER(S) { \