tools: mkimage: add support for gpimage format

This patch add support for gpimage format as a preparatory
patch for porting u-boot for keystone2 devices and is
based on omapimage format. It re-uses gph header to store the
size and loadaddr as done in omapimage.c

Signed-off-by: Vitaly Andrianov <vitalya@ti.com>
Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Acked-by: Tom Rini <trini@ti.com>
diff --git a/tools/imagetool.h b/tools/imagetool.h
index c2c9aea..a3e9d30 100644
--- a/tools/imagetool.h
+++ b/tools/imagetool.h
@@ -167,6 +167,7 @@
 void init_fit_image_type(void);
 void init_ubl_image_type(void);
 void init_omap_image_type(void);
+void init_gpimage_type(void);
 
 void pbl_load_uboot(int fd, struct image_tool_params *mparams);