binman: Respect pad-before property of section subentries

Other relevant properties (pad-after, offset, size, align, align-size,
align-end) already work since Pack() sets correct ranges for subentries'
data (.offset, .size variables), but some padding here is necessary to
align the data within this range to match the pad-before property.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

tools/binman/ftest.py

@@ -3483,5 +3483,13 @@ class TestFunctional(unittest.TestCase):
         expected = (U_BOOT_DATA + U_BOOT_DATA)
         self.assertEqual(expected, data)
 
+    def testPadInSections(self):
+        """Test pad-before, pad-after for entries in sections"""
+        data = self._DoReadFile('166_pad_in_sections.dts')
+        expected = (U_BOOT_DATA + tools.GetBytes(ord('!'), 12) +
+                    U_BOOT_DATA + tools.GetBytes(ord('!'), 6) +
+                    U_BOOT_DATA)
+        self.assertEqual(expected, data)
+
 if __name__ == "__main__":
     unittest.main()