usb: gadget: add usb3.0 descriptors to serial gadgets

This patch adds SS descriptors to the ACM & generic serial gadget. The
ACM part was tested with minicom + dummy + send / receive files over
ttyACM <=> ttyGS0.
The generic serial part (f_serial) was not tested (haven't found a
driver on the host side).
The nokia & multi gadget use HS at most.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/gadget/serial.c b/drivers/usb/gadget/serial.c
index ad9e5b2..665c074 100644
--- a/drivers/usb/gadget/serial.c
+++ b/drivers/usb/gadget/serial.c
@@ -242,7 +242,7 @@
 	.name		= "g_serial",
 	.dev		= &device_desc,
 	.strings	= dev_strings,
-	.max_speed	= USB_SPEED_HIGH,
+	.max_speed	= USB_SPEED_SUPER,
 };
 
 static int __init init(void)