binman: Allow text directly in the node

At present text entries use an indirect method to specify the text to use,
with a label pointing to the text itself.

Allow the text to be directly written into the node. This is more
convenient in cases where the text is constant.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/ftest.py b/tools/binman/ftest.py
index 8577adb..c74e12d 100644
--- a/tools/binman/ftest.py
+++ b/tools/binman/ftest.py
@@ -1286,7 +1286,7 @@
         expected = (tools.ToBytes(TEXT_DATA) +
                     tools.GetBytes(0, 8 - len(TEXT_DATA)) +
                     tools.ToBytes(TEXT_DATA2) + tools.ToBytes(TEXT_DATA3) +
-                    b'some text')
+                    b'some text' + b'more text')
         self.assertEqual(expected, data)
 
     def testEntryDocs(self):