gpu: nova-core: bitfield: Add support for custom visibility

gpu: nova-core: bitfield: Add support for custom visibility

Add support for custom visibility to allow for users to control
visibility of the structure and helpers.

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Elle Rhumsaa <elle@weathered-steel.dev>
Reviewed-by: Edwin Peer <epeer@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
[acourbot@nvidia.com: fix long lines warnings and typo in commit message.]
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Message-ID: <20251016151323.1201196-5-joelagnelf@nvidia.com>