patman: Move library functions into a library directory

The patman directory has a number of modules which are used by other tools
in U-Boot. This makes it hard to package the tools using pypi since the
common files must be copied along with the tool that uses them.

To address this, move these files into a new u_boot_pylib library. This
can be packaged separately and listed as a dependency of each tool.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/checkpatch.py b/tools/patman/checkpatch.py
index d1b902d..c1dec32 100644
--- a/tools/patman/checkpatch.py
+++ b/tools/patman/checkpatch.py
@@ -7,9 +7,9 @@
 import re
 import sys
 
-from patman import command
 from patman import gitutil
-from patman import terminal
+from u_boot_pylib import command
+from u_boot_pylib import terminal
 
 EMACS_PREFIX = r'(?:[0-9]{4}.*\.patch:[0-9]+: )?'
 TYPE_NAME = r'([A-Z_]+:)?'