Warnings or errors for parts not in db. Build pref csv only once.

Warnings or errors for parts not in db. Build pref csv only once.

Emit errors (or warnings with --warn-only) when filling parts from the
preferred DB.

Libreoffice doesn't like being run in parallel, so build the
preferred-parts.csv file only once and then use it in each of the
parts list generator rules.

Signed-off-by: Keith Packard <keithp@keithp.com>