patman: By default don't pass "--no-tree" to checkpatch for linux

When you pass "--no-tree" to checkpatch it disables some extra checks
that are important for Linux. Specifically I want checks like:

  warning: DT compatible string "boogie,woogie" appears un-documented
  check ./Documentation/devicetree/bindings/

Let's make the default for Linux to _not_ pass --no-tree. We'll have a
config option and command line flag to override.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/settings.py b/tools/patman/settings.py
index 4c847fe..903d6fc 100644
--- a/tools/patman/settings.py
+++ b/tools/patman/settings.py
@@ -23,6 +23,7 @@
     "u-boot": {},
     "linux": {
         "process_tags": "False",
+        "check_patch_use_tree": "True",
     },
     "gcc": {
         "process_tags": "False",
@@ -71,7 +72,7 @@
     >>> config = _ProjectConfigParser("linux")
     >>> config.readfp(StringIO(sample_config))
     >>> sorted((str(a), str(b)) for (a, b) in config.items("settings"))
-    [('am_hero', 'True'), ('process_tags', 'False')]
+    [('am_hero', 'True'), ('check_patch_use_tree', 'True'), ('process_tags', 'False')]
 
     # Check to make sure that settings works with unknown project.
     >>> config = _ProjectConfigParser("unknown")