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/common/image.c b/common/image.c
index 9c6bec5..fcc5a9c 100644
--- a/common/image.c
+++ b/common/image.c
@@ -125,6 +125,7 @@
 	{	IH_TYPE_FILESYSTEM, "filesystem", "Filesystem Image",	},
 	{	IH_TYPE_FIRMWARE,   "firmware",	  "Firmware",		},
 	{	IH_TYPE_FLATDT,     "flat_dt",    "Flat Device Tree",	},
+	{	IH_TYPE_GPIMAGE,    "gpimage",    "TI Keystone SPL Image",},
 	{	IH_TYPE_KERNEL,	    "kernel",	  "Kernel Image",	},
 	{	IH_TYPE_KERNEL_NOLOAD, "kernel_noload",  "Kernel Image (no loading done)", },
 	{	IH_TYPE_KWBIMAGE,   "kwbimage",   "Kirkwood Boot Image",},