rust: devres: require a bound device

Require the Bound device context to be able to a new Devres container.
This ensures that we can't register devres callbacks for unbound
devices.

Link: https://lore.kernel.org/r/20250413173758.12068-9-dakr@kernel.org


Signed-off-by: Danilo Krummrich <dakr@kernel.org>