rust: configfs: re-export configfs_attrs from configfs module

Re-export `configfs_attrs` from `configfs` module, so that users can import
the macro from the `configfs` module rather than the root of the `kernel`
crate.

Also update users to import from the new path.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250902-rnull-up-v6-16-v7-6-b5212cc89b98@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Andreas Hindborg

rust/kernel/configfs.rs

@@ -1039,3 +1039,5 @@ macro_rules! configfs_attrs {
     };
 
 }
+
+pub use crate::configfs_attrs;

samples/rust/rust_configfs.rs

@@ -5,7 +5,7 @@
 use kernel::alloc::flags;
 use kernel::c_str;
 use kernel::configfs;
-use kernel::configfs_attrs;
+use kernel::configfs::configfs_attrs;
 use kernel::new_mutex;
 use kernel::page::PAGE_SIZE;
 use kernel::prelude::*;