usb: gadget: f_sdp: Allow SPL to load and boot FIT via SDP

Add support for loading u-boot FIT images over the USB SDP protocol in
the SPL

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
[Various build fixes]
Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Tested-by: Fabio Estevam <festevam@gmail.com>
Tested-by: Lukasz Majewski <lukma@denx.de>
diff --git a/include/sdp.h b/include/sdp.h
index f6252d0..6ac64fb 100644
--- a/include/sdp.h
+++ b/include/sdp.h
@@ -10,6 +10,13 @@
 #define __SDP_H_
 
 int sdp_init(int controller_index);
-void sdp_handle(int controller_index);
+
+#ifdef CONFIG_SPL_BUILD
+#include <spl.h>
+
+int spl_sdp_handle(int controller_index, struct spl_image_info *spl_image);
+#else
+int sdp_handle(int controller_index);
+#endif
 
 #endif /* __SDP_H_ */