docs: conf.py: several coding style fixes

docs: conf.py: several coding style fixes

conf.py is missing a SPDX header and doesn't really have
a proper python coding style. It also has an obsolete
commented LaTeX syntax that doesn't work anymore.

Clean it up a little bit with some help from autolints
and manual adjustments.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/063c106d96e86ca30c3266f7819f30b7247881ed.1750571906.git.mchehab+huawei@kernel.org