u_boot_pylib: Move gitutil into the library

Move this file into U-Boot's Python library, so that it is no-longer
part of patman.

This makes a start on:

https://source.denx.de/u-boot/custodians/u-boot-dm/-/issues/35

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/__init__.py b/tools/patman/__init__.py
index 08eeffd..6de0e9f 100644
--- a/tools/patman/__init__.py
+++ b/tools/patman/__init__.py
@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0+
 
 __all__ = ['checkpatch', 'commit', 'control', 'func_test', 'get_maintainer',
-           'gitutil', '__main__', 'patchstream', 'project', 'series',
-           'settings','setup', 'status', 'test_checkpatch', 'test_settings']
+           '__main__', 'patchstream', 'project', 'series',
+           'settings', 'setup', 'status', 'test_checkpatch', 'test_settings']