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/bav335x.h b/include/configs/bav335x.h
index 741fb05..b53c49e 100644
--- a/include/configs/bav335x.h
+++ b/include/configs/bav335x.h
@@ -444,7 +444,7 @@
 #define CONFIG_MUSB_PIO_ONLY
 #define CONFIG_MUSB_DISABLE_BULK_COMBINE_SPLIT
 #define CONFIG_USB_GADGET
-#define CONFIG_USBDOWNLOAD_GADGET
+#define CONFIG_USB_GADGET_DOWNLOAD
 #define CONFIG_USB_GADGET_DUALSPEED
 #define CONFIG_USB_GADGET_VBUS_DRAW	2
 #define CONFIG_MUSB_HOST
@@ -472,7 +472,7 @@
 
 #ifdef CONFIG_MUSB_GADGET
 #define CONFIG_CMD_USB_MASS_STORAGE
-#define CONFIG_USB_GADGET_MASS_STORAGE
+#define CONFIG_USB_FUNCTION_MASS_STORAGE
 
 /* USB TI's IDs */
 #define CONFIG_G_DNL_VENDOR_NUM 0x0451
@@ -494,7 +494,7 @@
 
 /* USB Device Firmware Update support */
 #ifndef CONFIG_SPL_BUILD
-#define CONFIG_DFU_FUNCTION
+#define CONFIG_USB_FUNCTION_DFU
 #define CONFIG_DFU_MMC
 #define CONFIG_CMD_DFU
 #define DFU_ALT_INFO_MMC \