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/dra7xx_evm.h b/include/configs/dra7xx_evm.h
index 0323c72..b969944 100644
--- a/include/configs/dra7xx_evm.h
+++ b/include/configs/dra7xx_evm.h
@@ -190,7 +190,7 @@
 #define CONFIG_USB_DWC3_GADGET
 
 #define CONFIG_USB_GADGET
-#define CONFIG_USBDOWNLOAD_GADGET
+#define CONFIG_USB_GADGET_DOWNLOAD
 #define CONFIG_USB_GADGET_VBUS_DRAW 2
 #define CONFIG_G_DNL_MANUFACTURER "Texas Instruments"
 #define CONFIG_G_DNL_VENDOR_NUM 0x0451
@@ -198,7 +198,7 @@
 #define CONFIG_USB_GADGET_DUALSPEED
 
 /* USB Device Firmware Update support */
-#define CONFIG_DFU_FUNCTION
+#define CONFIG_USB_FUNCTION_DFU
 #define CONFIG_DFU_RAM
 #define CONFIG_CMD_DFU