usb: USB download gadget and functions config options coherent naming

This introduces a coherent scheme for naming USB download gadget and functions
config options. The download USB gadget config option is moved to
CONFIG_USB_GADGET_DOWNLOAD for better consistency with other gadgets and each
function's config option is moved to a CONFIG_USB_FUNCTION_ prefix.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Tested-by: Lukasz Majewski <l.majewski@samsung.com>

Test HW: Odroid_XU3 (Exynos5422), trats (Exynos4210)
diff --git a/include/configs/gw_ventana.h b/include/configs/gw_ventana.h
index 902ec2c..2cbd5e0 100644
--- a/include/configs/gw_ventana.h
+++ b/include/configs/gw_ventana.h
@@ -205,8 +205,8 @@
 /* USB Mass Storage Gadget */
 #define CONFIG_USB_GADGET
 #define CONFIG_CMD_USB_MASS_STORAGE
-#define CONFIG_USB_GADGET_MASS_STORAGE
-#define CONFIG_USBDOWNLOAD_GADGET
+#define CONFIG_USB_FUNCTION_MASS_STORAGE
+#define CONFIG_USB_GADGET_DOWNLOAD
 #define CONFIG_USB_GADGET_VBUS_DRAW    2
 
 /* Netchip IDs */