dtoc: Decode val if it's a byte string

With Python 3.5.2 encode will throw an exception if val is a byte array.
Decode it to a string first. This assumes it's utf-8, if it's not valid
utf-8 it will throw an exception.

Signed-off-by: George McCollister <george.mccollister@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>

tools/dtoc/fdt_util.py

@@ -24,6 +24,8 @@ def fdt32_to_cpu(val):
         A native-endian integer value
     """
     if sys.version_info > (3, 0):
+        if isinstance(val, bytes):
+            val = val.decode('utf-8')
         val = val.encode('raw_unicode_escape')
     return struct.unpack('>I', val)[0]