usb: gadget: add isoch_delay member

Whenever a USB host issues a Set Isoch Delay request, we should cache
the result so relevant gadget drivers can make use of the value for
calculating how many uFrames ahead a transfer should be queued.
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

include/linux/usb/gadget.h

@@ -330,6 +330,7 @@ struct usb_gadget_ops {
  * @name: Identifies the controller hardware type.  Used in diagnostics
  *	and sometimes configuration.
  * @dev: Driver model state for this abstract device.
+ * @isoch_delay: value from Set Isoch Delay request. Only valid on SS/SSP
  * @out_epnum: last used out ep number
  * @in_epnum: last used in ep number
  * @mA: last set mA value
@@ -394,6 +395,7 @@ struct usb_gadget {
 	enum usb_device_state		state;
 	const char			*name;
 	struct device			dev;
+	unsigned			isoch_delay;
 	unsigned			out_epnum;
 	unsigned			in_epnum;
 	unsigned			mA;