usb: gadget: net2280: Add support for PLX USB338X

This patch adds support for the PLX USB3380 and USB3382.

This driver is based on the driver from the manufacturer.

Since USB338X is register compatible with NET2280, I thought that it
would be better to include this hardware into net2280 driver.

Manufacturer's driver only supported the USB33X, did not follow the
Kernel Style and contain some trivial errors. This patch has tried to
address this issues.

This patch has only been tested on USB338x hardware, but the merge has
been done trying to not affect the behaviour of NET2280.

Tested-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/Kconfig

@@ -409,7 +409,7 @@ config USB_NET2272_DMA
 	  If unsure, say "N" here.  The driver works fine in PIO mode.
 
 config USB_NET2280
-	tristate "NetChip 228x"
+	tristate "NetChip 228x / PLX USB338x"
 	depends on PCI
 	help
 	   NetChip 2280 / 2282 is a PCI based USB peripheral controller which
@@ -419,6 +419,14 @@ config USB_NET2280
 	   (for control transfers) and several endpoints with dedicated
 	   functions.
 
+	   PLX 3380 / 3382 is a PCIe based USB peripheral controller which
+	   supports full, high speed USB 2.0 and super speed USB 3.0
+	   data transfers.
+
+	   It has eight configurable endpoints, as well as endpoint zero
+	   (for control transfers) and several endpoints with dedicated
+	   functions.
+
 	   Say "y" to link the driver statically, or "m" to build a
 	   dynamically linked module called "net2280" and force all
 	   gadget drivers to also be dynamically linked.