dma-fence: Add helpers for accessing driver and timeline name

dma-fence: Add helpers for accessing driver and timeline name

Add some helpers in order to enable preventing dma-fence users accessing
the implementation details directly and make the implementation itself use
them.

This will also enable later adding some asserts to a consolidated
location.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Tvrtko Ursulin <tursulin@ursulin.net>
Link: https://lore.kernel.org/r/20250515095004.28318-4-tvrtko.ursulin@igalia.com