binman: Add support for calling mkimage

As a first step to integrating mkimage into binman, add a new entry type
that feeds data into mkimage for processing and incorporates that output
into the image.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/ftest.py b/tools/binman/ftest.py
index 5e24920..39e67b9 100644
--- a/tools/binman/ftest.py
+++ b/tools/binman/ftest.py
@@ -3357,6 +3357,13 @@
         data = self._DoReadFile('154_intel_fsp_t.dts')
         self.assertEqual(FSP_T_DATA, data[:len(FSP_T_DATA)])
 
+    def testMkimage(self):
+        """Test using mkimage to build an image"""
+        data = self._DoReadFile('156_mkimage.dts')
+
+        # Just check that the data appears in the file somewhere
+        self.assertIn(U_BOOT_SPL_DATA, data)
+
 
 if __name__ == "__main__":
     unittest.main()