treewide: Drop image_header_t typedef

This is not needed and we should avoid typedefs. Use the struct instead
and rename it to indicate that it really is a legacy struct.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/ftest.py b/tools/binman/ftest.py
index ecb3595..261107b 100644
--- a/tools/binman/ftest.py
+++ b/tools/binman/ftest.py
@@ -5782,7 +5782,7 @@
         # Check that the data appears in the file somewhere
         self.assertIn(U_BOOT_SPL_DATA, data)
 
-        # Get struct image_header -> ih_name
+        # Get struct legacy_img_hdr -> ih_name
         name = data[0x20:0x40]
 
         # Build the filename that we expect to be placed in there, by virtue of
@@ -5799,7 +5799,7 @@
         # Check that the data appears in the file somewhere
         self.assertIn(U_BOOT_SPL_DATA, data)
 
-        # Get struct image_header -> ih_name
+        # Get struct legacy_img_hdr -> ih_name
         name = data[0x20:0x40]
 
         # Build the filename that we expect to be placed in there, by virtue of