usb:g_dnl:dfu: Download gadget and DFU function code clean up

The download gadget code and DFU function lacks of proper declarations
for the case when a target board wants to use only one of available usb
functions.

Moreover the relevant declarations have been moved to consistent
localization (like <dfu.h>).

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Cc: Marek Vasut <marex@denx.de>

drivers/usb/gadget/f_dfu.h

@@ -82,7 +82,4 @@ struct dfu_function_descriptor {
 	__le16				wTransferSize;
 	__le16				bcdDFUVersion;
 } __packed;
-
-/* configuration-specific linkup */
-int dfu_add(struct usb_configuration *c);
 #endif /* __F_DFU_H_ */

drivers/usb/gadget/g_dnl.c

@@ -15,7 +15,7 @@
 
 #include <g_dnl.h>
 #include <usb_mass_storage.h>
-#include "f_dfu.h"
+#include <dfu.h>
 
 #include "gadget_chips.h"
 #include "composite.c"

include/dfu.h

@@ -14,6 +14,7 @@
 #include <common.h>
 #include <linux/list.h>
 #include <mmc.h>
+#include <linux/usb/composite.h>
 
 enum dfu_device_type {
 	DFU_DEV_MMC = 1,
@@ -161,4 +162,12 @@ static inline int dfu_fill_entity_ram(struct dfu_entity *dfu, char *s)
 }
 #endif
 
+#ifdef CONFIG_DFU_FUNCTION
+int dfu_add(struct usb_configuration *c);
+#else
+int dfu_add(struct usb_configuration *c)
+{
+	return 0;
+}
+#endif
 #endif /* __DFU_ENTITY_H_ */