rust: lock: introduce Mutex

This is the `struct mutex` lock backend and allows Rust code to use the
kernel mutex idiomatically.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
Link: https://lore.kernel.org/r/20230411054543.21278-3-wedsonaf@gmail.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/kernel/sync/lock.rs

@@ -10,6 +10,8 @@ use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque};
 use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned};
 use macros::pin_data;
 
+pub mod mutex;
+
 /// The "backend" of a lock.
 ///
 /// It is the actual implementation of the lock, without the need to repeat patterns used in all