rust: revocable: indicate whether `data` has been revoked already

Return a boolean from Revocable::revoke() and Revocable::revoke_nosync()
to indicate whether the data has been revoked already.

Return true if the data hasn't been revoked yet (i.e. this call revoked
the data), false otherwise.

This is required by Devres in order to synchronize the completion of the
revoke process.

Reviewed-by: Benno Lossin <lossin@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://lore.kernel.org/r/20250612121817.1621-3-dakr@kernel.org


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