dtoc: Use byte type instead of str in fdt

In Python 3 bytes and str are separate types. Use bytes to ensure that
the code functions correctly with Python 3.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/tools.py b/tools/patman/tools.py
index 976670e..bdc1953 100644
--- a/tools/patman/tools.py
+++ b/tools/patman/tools.py
@@ -317,3 +317,28 @@
         byte: A byte or str value
     """
     return chr(byte) if type(byte) != str else byte
+
+def ToChars(byte_list):
+    """Convert a list of bytes to a str/bytes type
+
+    Args:
+        byte_list: List of ASCII values representing the string
+
+    Returns:
+        string made by concatenating all the ASCII values
+    """
+    return ''.join([chr(byte) for byte in byte_list])
+
+def ToBytes(string):
+    """Convert a str type into a bytes type
+
+    Args:
+        string: string to convert value
+
+    Returns:
+        Python 3: A bytes type
+        Python 2: A string type
+    """
+    if sys.version_info[0] >= 3:
+        return string.encode('utf-8')
+    return string