dtoc: Move BytesToValue() and GetEmpty() into PropBase

These functions are currently in a separate fdt_util file. Since they are
only used from PropBase and subclasses, it makes sense for them to be in the
PropBase class.

Move these functions into fdt.py along with the list of types.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/dtoc/dtoc.py b/tools/dtoc/dtoc.py
index 10f6a12..518aa51 100755
--- a/tools/dtoc/dtoc.py
+++ b/tools/dtoc/dtoc.py
@@ -16,6 +16,7 @@
 our_path = os.path.dirname(os.path.realpath(__file__))
 sys.path.append(os.path.join(our_path, '../patman'))
 
+import fdt
 import fdt_select
 import fdt_util
 
@@ -33,10 +34,10 @@
 
 # C type declarations for the tyues we support
 TYPE_NAMES = {
-    fdt_util.TYPE_INT: 'fdt32_t',
-    fdt_util.TYPE_BYTE: 'unsigned char',
-    fdt_util.TYPE_STRING: 'const char *',
-    fdt_util.TYPE_BOOL: 'bool',
+    fdt.TYPE_INT: 'fdt32_t',
+    fdt.TYPE_BYTE: 'unsigned char',
+    fdt.TYPE_STRING: 'const char *',
+    fdt.TYPE_BOOL: 'bool',
 };
 
 STRUCT_PREFIX = 'dtd_'
@@ -138,13 +139,13 @@
             type: Data type (fdt_util)
             value: Data value, as a string of bytes
         """
-        if type == fdt_util.TYPE_INT:
+        if type == fdt.TYPE_INT:
             return '%#x' % fdt_util.fdt32_to_cpu(value)
-        elif type == fdt_util.TYPE_BYTE:
+        elif type == fdt.TYPE_BYTE:
             return '%#x' % ord(value[0])
-        elif type == fdt_util.TYPE_STRING:
+        elif type == fdt.TYPE_STRING:
             return '"%s"' % value
-        elif type == fdt_util.TYPE_BOOL:
+        elif type == fdt.TYPE_BOOL:
             return 'true'
 
     def GetCompatName(self, node):