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>
diff --git a/tools/mkimage.h b/tools/mkimage.h
index ec67336..9033a7d 100644
--- a/tools/mkimage.h
+++ b/tools/mkimage.h
@@ -140,6 +140,7 @@
  * Supported image types init functions
  */
 void init_kwb_image_type (void);
+void init_imx_image_type (void);
 void init_default_image_type (void);
 void init_fit_image_type (void);