doc: conf: add common test preparation imports

When adding test setup blocks, we need some imports over and over again.
Let's import them here to keep the test setup blocks as small as
possible.

Signed-off-by: Bastian Krause <bst@pengutronix.de>

Author: Bastian-Krause

doc/conf.py

@@ -209,6 +209,8 @@ def setup(app):
 
 doctest_global_setup = '''
 import os
+import shutil
+from unittest.mock import Mock, patch
 
 doctest_dir = '.build/doctest'