Documentation: Start translations to Spanish

Start the process of translating kernel documentation to Spanish. Create
directory sp_SP/ instead of es_ES/ (diverging from format of prior
translated directories) since this directory should accept any dialects of
Spanish. Include an index and a disclaimer, following the approach of
prior translations. Add Carlos Bilbao as MAINTAINER of this effort.

Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Carlos Bilbao <carlos.bilbao@amd.com>
Link: https://lore.kernel.org/r/20221024145521.69465-2-carlos.bilbao@amd.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>