docs/sp_SP: Move howto.rst into /sp_SP/process/

Move the howto.rst file in Spanish translation to /sp_SP/process/ to
ensure its location is symmetrical to its corresponding version in
English.

Signed-off-by: Avadhut Naik <avadhut.naik@amd.com>
Reviewed-by: Carlos Bilbao <carlos.bilbao@amd.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231211023730.2026204-5-avadhut.naik@amd.com