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/odroid_xu3.h b/include/configs/odroid_xu3.h
index cf17f3d..8d5c736 100644
--- a/include/configs/odroid_xu3.h
+++ b/include/configs/odroid_xu3.h
@@ -60,10 +60,10 @@
 #define CONFIG_G_DNL_VENDOR_NUM		0x04E8
 #define CONFIG_G_DNL_PRODUCT_NUM	0x6601
 #define CONFIG_G_DNL_MANUFACTURER	"Samsung"
-#define CONFIG_USBDOWNLOAD_GADGET
+#define CONFIG_USB_GADGET_DOWNLOAD
 
 /* DFU */
-#define CONFIG_DFU_FUNCTION
+#define CONFIG_USB_FUNCTION_DFU
 #define CONFIG_DFU_MMC
 #define CONFIG_CMD_DFU
 #define CONFIG_SYS_DFU_DATA_BUF_SIZE	SZ_32M
@@ -72,13 +72,13 @@
 /* THOR */
 #define CONFIG_G_DNL_THOR_VENDOR_NUM	CONFIG_G_DNL_VENDOR_NUM
 #define CONFIG_G_DNL_THOR_PRODUCT_NUM	0x685D
-#define CONFIG_THOR_FUNCTION
+#define CONFIG_USB_FUNCTION_THOR
 #define CONFIG_CMD_THOR_DOWNLOAD
 
 /* UMS */
 #define CONFIG_G_DNL_UMS_VENDOR_NUM	0x0525
 #define CONFIG_G_DNL_UMS_PRODUCT_NUM	0xA4A5
-#define CONFIG_USB_GADGET_MASS_STORAGE
+#define CONFIG_USB_FUNCTION_MASS_STORAGE
 #define CONFIG_CMD_USB_MASS_STORAGE
 
 /* FIXME: MUST BE REMOVED AFTER TMU IS TURNED ON */