Add support in `CSR` configuration for user-defined access types

### Motivation

Different users of CSRs may have their own special ways of managing access types for registers. Sometimes that might imply a different way of accessing in generated hardware, and other times it might just be a matter of configuration for similar hardware.

### Desired solution

Add a way for users to extend the types of access types supported for CSR configuration and hardware generation.

### Alternatives considered

_No response_

### Additional details

_No response_