rust: device: implement FwNode::is_of_node()

Implement FwNode::is_of_node() in order to check whether a FwNode
instance is embedded in a struct device_node.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Igor Korotin <igor.korotin.linux@gmail.com>
Link: https://lore.kernel.org/r/20250620151504.278766-1-igor.korotin.linux@gmail.com


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