dm: Add a test for of-platdata

Add a simple test which checks that the of-platdata system is working
correctly. The sequence is as follows:

- SPL starts up and probes all the UCLASS_MISC drivers
- There are 3 of these in sandbox.dts
- Therefore there should be 3 U_BOOT_DEVICE() declarations in dt-platdata.c
- These should produce 3 sandbox_spl_test devices
- Each device prints out its platform data when probed
- This test checks for this output and compares it against expectations

Signed-off-by: Simon Glass <sjg@chromium.org>

test/py/tests/test_ofplatdata.py

+# Copyright (c) 2016 Google, Inc
+#
+# SPDX-License-Identifier: GPL-2.0+
+
+import pytest
+
+OF_PLATDATA_OUTPUT = '''
+of-platdata probe:
+bool 1
+byte 05
+bytearray 06 00 00
+int 1
+intarray 2 3 4 0
+longbytearray 09 0a 0b 0c 0d 0e 0f 10 11
+string message
+stringarray "multi-word" "message" ""
+of-platdata probe:
+bool 0
+byte 08
+bytearray 01 23 34
+int 3
+intarray 5 0 0 0
+longbytearray 09 00 00 00 00 00 00 00 00
+string message2
+stringarray "another" "multi-word" "message"
+of-platdata probe:
+bool 0
+byte 00
+bytearray 00 00 00
+int 0
+intarray 0 0 0 0
+longbytearray 00 00 00 00 00 00 00 00 00
+string <NULL>
+stringarray "one" "" ""
+'''
+
+@pytest.mark.buildconfigspec('spl')
+def test_ofplatdata(u_boot_console):
+    """Test that of-platdata can be generated and used in sandbox"""
+    cons = u_boot_console
+    output = cons.get_spawn_output().replace('\r', '')
+    assert OF_PLATDATA_OUTPUT in output