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/tbs2910.h b/include/configs/tbs2910.h
index 42e5821..397c95c 100644
--- a/include/configs/tbs2910.h
+++ b/include/configs/tbs2910.h
@@ -133,10 +133,10 @@
 #define CONFIG_CI_UDC
 #define CONFIG_USBD_HS
 #define CONFIG_USB_GADGET
-#define CONFIG_USB_GADGET_MASS_STORAGE
+#define CONFIG_USB_FUNCTION_MASS_STORAGE
 #define CONFIG_USB_GADGET_DUALSPEED
 #define CONFIG_USB_GADGET_VBUS_DRAW	0
-#define CONFIG_USBDOWNLOAD_GADGET
+#define CONFIG_USB_GADGET_DOWNLOAD
 #define CONFIG_G_DNL_VENDOR_NUM		0x0525
 #define CONFIG_G_DNL_PRODUCT_NUM	0xa4a5
 #define CONFIG_G_DNL_MANUFACTURER	"TBS"