Revert "usb: gadget: allow to enable legacy drivers without USB_ETH"

This reverts commit 7a9618a2.

Romain Izard recently reported that commit 7a9618a2 ended up
allowing every legacy gadget driver to statically linked to the
kernel, however that doesn't work, since only one legacy gadget can be
bound to a controller. Because of that, let's revert the original commit
and fix the problem.
Reported-by: Romain Izard <romain.izard.pro@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/Kconfig

@@ -508,8 +508,8 @@ choice
 	  controller, and the relevant drivers for each function declared
 	  by the device.
 
-endchoice
-
 source "drivers/usb/gadget/legacy/Kconfig"
 
+endchoice
+
 endif # USB_GADGET

drivers/usb/gadget/legacy/Kconfig

@@ -13,14 +13,6 @@
 # both kinds of controller can also support "USB On-the-Go" (CONFIG_USB_OTG).
 #
 
-menuconfig USB_GADGET_LEGACY
-	bool "Legacy USB Gadget Support"
-	help
-	   Legacy USB gadgets are USB gadgets that do not use the USB gadget
-	   configfs interface.
-
-if USB_GADGET_LEGACY
-
 config USB_ZERO
 	tristate "Gadget Zero (DEVELOPMENT)"
 	select USB_LIBCOMPOSITE
@@ -498,5 +490,3 @@ config USB_G_WEBCAM
 
 	  Say "y" to link the driver statically, or "m" to build a
 	  dynamically linked module called "g_webcam".
-
-endif