[FIX] base_vat: Add support for MVA suffix in Norwegian VAT numbers.

Description of the issue/feature this PR addresses:
The Tax ID field is validating NOxxxxxxxxx as format, but the format is actually NOxxxxxxxxxMVA if you are in the VAT registrty.

Current behavior before PR:
Valid tax numbers for Norway are rejected.

Desired behavior after PR is merged:
The format NOxxxxxxxxxMVA is accepted, along with the old behaviour of NOxxxxxxxxx.