binman: Update entry_test to support Python 3

The reload() function is in a different place in Python 3. Update the code
to handle this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/entry_test.py b/tools/binman/entry_test.py
index 1f7ff5b..b30a7be 100644
--- a/tools/binman/entry_test.py
+++ b/tools/binman/entry_test.py
@@ -41,7 +41,11 @@
         del sys.modules['importlib']
         global entry
         if entry:
-            reload(entry)
+            if sys.version_info[0] >= 3:
+                import importlib
+                importlib.reload(entry)
+            else:
+                reload(entry)
         else:
             import entry
         entry.Entry.Create(None, self.GetNode(), 'u-boot-spl')