patman: Convert camel case in gitutil.py

Convert this file to snake case and update all files which use it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/builderthread.py b/tools/buildman/builderthread.py
index 90099ee..7522ff6 100644
--- a/tools/buildman/builderthread.py
+++ b/tools/buildman/builderthread.py
@@ -219,7 +219,7 @@
                     commit = self.builder.commits[commit_upto]
                     if self.builder.checkout:
                         git_dir = os.path.join(work_dir, '.git')
-                        gitutil.Checkout(commit.hash, git_dir, work_dir,
+                        gitutil.checkout(commit.hash, git_dir, work_dir,
                                          force=True)
                 else:
                     commit = 'current'