pylibfdt: Add a method to access the device tree directly

When calling libfdt functions which are not supported by the Fdt class it
is necessary to get direct access to the device tree data. At present this
requries using the internal _fdt member. Add a new method to provide
public access to this, without allowing the data to be changed.

Note that a bytearray type is returned rather than str, since the swig
types are set up for bytearray to map correctly to const void *.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/pylibfdt_tests.py

@@ -297,9 +297,10 @@ class PyLibfdtTests(unittest.TestCase):
 
     def testIntegers(self):
         """Check that integers can be passed and returned"""
-        self.assertEquals(0, libfdt.fdt_get_phandle(self.fdt._fdt, 0))
+        self.assertEquals(0, libfdt.fdt_get_phandle(self.fdt.as_bytearray(), 0))
         node2 = self.fdt.path_offset('/subnode@2')
-        self.assertEquals(0x2000, libfdt.fdt_get_phandle(self.fdt._fdt, node2))
+        self.assertEquals(
+                0x2000, libfdt.fdt_get_phandle(self.fdt.as_bytearray(), node2))
 
     def testGetPhandle(self):
         """Test for the get_phandle() method"""