VAT validation for greek VAT IDs always fails

[theroch]

Preconditions (*)

1. Any OpenMage version up to latest
2. Shippable product
3. Tax calculation by shipping address is configured

Steps to reproduce (*)

1. Add a customer from greek country with greek vat id like EL123456789 (without EL) and try to register
2. Tryf to order something without tax.

Expected result (*)

1. VAT validation is successful

Actual result (*)

1. VAT validation fails always

More information:
OpenMage uses the the ISO-2 country ID for VAT validation but for Greek the country ID is not GR but EL.

https://steemit.com/magento/@svosse/vat-validation-not-working-for-greek-customers-magento
https://github.com/magento/magento2/pull/20548/files/3ed5efb6d43067132dd10dd01579461513e3e7ef#diff-e40dc6a5b6185326ffe0e8a77186fad3401d8f791d2a61b68c37aa924fd10cb5

We will backport the Magento 2 fix.