Makefile: Add a pylint checker to the build

At present the Python code in U-Boot is somewhat inconsistent, with some
files passing pylint quite cleanly and others not.

Add a way to track progress on this clean-up, by checking that no module
has got any worse as a result of changes.

This can be used with 'make pylint'.

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Re-generate pylint.base]

scripts/pylint.base

@@ -0,0 +1,215 @@
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