scripts/sphinx-pre-install: allow checking for multiple missing files

The current implementation take a simple file as first argument, this
change allows to take a list as a first argument.

Some file could have a different path according distribution version

Signed-off-by: Jeremy MAURO <j.mauro@criteo.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>