patman: Tidy up sys.path changes

Now that we are using absolute paths we can remove some of the sys.path
mangling that appears in the tools.

We only need to add the path to 'tools/' so that everything can find
modules relative to that directory.

The special paths for finding pylibfdt remain.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/main.py b/tools/patman/main.py
index f59367f..f3d9c0c 100755
--- a/tools/patman/main.py
+++ b/tools/patman/main.py
@@ -13,7 +13,7 @@
 import unittest
 
 if __name__ == "__main__":
-    # Allow 'import xxx to work'
+    # Allow 'from patman import xxx to work'
     our_path = os.path.dirname(os.path.realpath(__file__))
     sys.path.append(os.path.join(our_path, '..'))