rust: configfs: introduce rust support for configfs

Add a Rust API for configfs, thus allowing Rust modules to use configfs for
configuration. Make the implementation a shim on top of the C configfs
implementation, allowing safe use of the C infrastructure from Rust.

Link: https://lore.kernel.org/r/20250508-configfs-v8-1-8ebde6180edc@kernel.org
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>

rust/kernel/lib.rs

@@ -42,6 +42,8 @@ pub mod alloc;
 pub mod block;
 #[doc(hidden)]
 pub mod build_assert;
+#[cfg(CONFIG_CONFIGFS_FS)]
+pub mod configfs;
 pub mod cred;
 pub mod device;
 pub mod device_id;