gpu: nova-core: register: improve `Debug` implementation

gpu: nova-core: register: improve `Debug` implementation

Now that we have an internal rule to dispatch field information where
needed, use it to generate a better `Debug` implementation where the raw
hexadecimal value of the register is displayed, as well as the `Debug`
values of its individual fields.

Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://lore.kernel.org/r/20250718-nova-regs-v2-11-7b6a762aa1cd@nvidia.com
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>