ipq807x: Add support to use defined mkimage for creating U-boot image.

Change-Id: I61f9f3b5baeb9bfb854f7a48b6ccdb7d912fdca7
Signed-off-by: Pavithra Palanisamy <pavip@codeaurora.org>
diff --git a/tools/pack.py b/tools/pack.py
index 040558d..f168685 100644
--- a/tools/pack.py
+++ b/tools/pack.py
@@ -1287,7 +1287,7 @@
         its_fp.close()
 	
         try:
-            cmd = ["mkimage", "-f", self.its_fname, self.img_fname]
+            cmd = [SRC_DIR + "/mkimage", "-f", self.its_fname, self.img_fname]
             ret = subprocess.call(cmd)
             if ret != 0:
                 print ret