[dv] csr exclusion enhancement

Recently we have fixed a few issues to due putting csr write exclusion to a field.
Here are two solutions:
1). Return an error once we found a write exclusion is applied to the field.
2). Support csr write field exclusion -
since there is no partial write, supporting this feature can be tricky. I was thinking to just write default/reset value when this field is excluded from write, but it might have some side effect.

Please let me know what you think.

Start by reviewing the existing CSR write-exclusion fixes referenced in the issue and the surrounding design-verification behavior. Decide whether exclusion should report an error or write the default/reset value, document the side effects, and define tests that demonstrate the chosen behavior.

Written by the indexing model from the issue text.