rust: regulator: implement Send and Sync for Regulator<T>

Sending a &Regulator<T> to another thread is safe, as the regulator core
will properly handle the locking for us. Additionally, there are no
restrictions that prevents sending a Regulator<T> to another thread.

Given these two facts, implement Send and Sync.

Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://patch.msgid.link/20250729-regulator-send-sync-v1-2-8bcbd546b940@collabora.com


Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Mark Brown <broonie@kernel.org>