rust: platform: impl Send + Sync for platform::Device

Commit 4d320e3 ("rust: platform: fix unrestricted &mut
platform::Device") changed the definition of platform::Device and
discarded the implicitly derived Send and Sync traits.

This isn't required by upstream code yet, and hence did not cause any
issues. However, it is relied on by upcoming drivers, hence add it back
in.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20250318212940.137577-2-dakr@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Danilo Krummrich

rust/kernel/platform.rs

@@ -233,3 +233,10 @@ impl AsRef<device::Device> for Device {
         unsafe { device::Device::as_ref(dev) }
     }
 }
+
+// SAFETY: A `Device` is always reference-counted and can be released from any thread.
+unsafe impl Send for Device {}
+
+// SAFETY: `Device` can be shared among threads because all methods of `Device`
+// (i.e. `Device<Normal>) are thread safe.
+unsafe impl Sync for Device {}