rust: block: introduce kernel::block::mq module

Add initial abstractions for working with blk-mq.

This patch is a maintained, refactored subset of code originally published
by Wedson Almeida Filho <wedsonaf@gmail.com> [1].

[1] f2cfd2fe0e/rust/kernel/blk/mq.rs

Cc: Wedson Almeida Filho <wedsonaf@gmail.com>
Signed-off-by: Andreas Hindborg <a.hindborg@samsung.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20240611114551.228679-2-nmi@metaspace.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>

rust/kernel/error.rs

@@ -126,6 +126,12 @@ impl Error {
         self.0
     }
 
+    #[cfg(CONFIG_BLOCK)]
+    pub(crate) fn to_blk_status(self) -> bindings::blk_status_t {
+        // SAFETY: `self.0` is a valid error due to its invariant.
+        unsafe { bindings::errno_to_blk_status(self.0) }
+    }
+
     /// Returns the error encoded as a pointer.
     #[allow(dead_code)]
     pub(crate) fn to_ptr<T>(self) -> *mut T {