scripts/xls_to_doc.py: ignore fields filled by lists by default

Currently, some parmeters like Run Type are imported from files.
Don't add documentation for them by default, preserving the way
it was originally meant to be filled.

Acked-by: Katarzyna Piecielska <katarzyna.piecielska@intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>