[FIX] models: add xmlid for inherited selection values

If model A has a selection field, and is inherited by 2 modules
B and C, B adds selection values to the field, and C inherits model
A under a different module and model names.
Based on the order of installation of B and C, we may end up with
different xmlids.
If B is installed before C, then B will add xmlids for the new
selection values added for model C. But if C is installed before
B, then C will have the selection values from B without xmlids.
The change here ensures that the selection values introduced by B
will always have correct xmlids.

closes odoo/odoo#127251

Signed-off-by: Raphael Collet <rco@odoo.com>