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/siemens-am33x-common.h b/include/configs/siemens-am33x-common.h
index e5fd147..f33f9b4 100644
--- a/include/configs/siemens-am33x-common.h
+++ b/include/configs/siemens-am33x-common.h
@@ -249,7 +249,7 @@
 #endif /* CONFIG_MUSB_GADGET */
 
 #define CONFIG_USB_GADGET
-#define CONFIG_USBDOWNLOAD_GADGET
+#define CONFIG_USB_GADGET_DOWNLOAD
 
 /* USB DRACO ID as default */
 #define CONFIG_USBD_HS
@@ -258,7 +258,7 @@
 #define CONFIG_G_DNL_MANUFACTURER "Siemens AG"
 
 /* USB Device Firmware Update support */
-#define CONFIG_DFU_FUNCTION
+#define CONFIG_USB_FUNCTION_DFU
 #define CONFIG_DFU_NAND
 #define CONFIG_CMD_DFU
 #define CONFIG_SYS_DFU_DATA_BUF_SIZE	(1 << 20)