board: stm32mp1: board: add include for dfu

Add include for dfu, add prototype for set_dfu_alt_info
and avoid warning when compiling with W=1.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>

board/st/stm32mp1/stm32mp1.c

@@ -7,6 +7,7 @@
 #include <bootm.h>
 #include <clk.h>
 #include <config.h>
+#include <dfu.h>
 #include <dm.h>
 #include <env.h>
 #include <env_internal.h>