mkimage: Add Freescale imx Boot Image support (imximage)

This patch adds support for "imximage" (MX Boot Image)
to the mkimage utility. The imximage is used on the Freescales's
MX.25, MX.35 and MX.51 processors.

Further details under doc/README.imximage.

This patch was tested on a Freescale mx51evk board.

Signed-off-by: Stefano Babic <sbabic@denx.de>

common/image.c

@@ -140,6 +140,7 @@ static table_entry_t uimage_type[] = {
 	{	IH_TYPE_STANDALONE, "standalone", "Standalone Program", },
 	{	IH_TYPE_FLATDT,     "flat_dt",    "Flat Device Tree",	},
 	{	IH_TYPE_KWBIMAGE,   "kwbimage",   "Kirkwood Boot Image",},
+	{	IH_TYPE_IMXIMAGE,   "imximage",   "Freescale i.MX Boot Image",},
 	{	-1,		    "",		  "",			},
 };