rust: device: Add property_get_reference_args

Allow Rust code to read reference args from device properties. The
wrapper type `FwNodeReferenceArgs` allows callers to access the buffer
of read args safely.

Signed-off-by: Remo Senekowitsch <remo@buenzli.dev>
Link: https://lore.kernel.org/r/20250616154511.1862909-3-remo@buenzli.dev


[ Move up NArgs; refer to FwNodeReferenceArgs in NArgs doc-comment.
  - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>