Use attribute accessor functions in driver wrappers

Fully automated:
```
perl -i -pe 's/(\w+)->core\.(\w+)/psa_get_key_$2($1)/g' scripts/data_files/driver_templates/*.jinja docs/psa-driver-example-and-guide.md
```

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>