scripts/xls_to_doc.py: don't be verbose by default

Add a verbosity parameter to hide messages used mostly for debugging
purposes, as, on several cases, the output may be misleading.

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