rust: sync: Make Guard::new() public

Since we added a `Lock::from_raw()` function previously, it makes sense
to also introduce an interface for creating a `Guard` from a reference
to a `Lock` for instances where we've derived the `Lock` from a raw
pointer and know that the lock is already acquired, there are such
usages in KMS API.

[Boqun: Add backquotes to type names, reformat the commit log, reword a
 bit on the usage of KMS API]

Signed-off-by: Lyude Paul <[email protected]>
Reviewed-by: Filipe Xavier <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Signed-off-by: Boqun Feng <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: Lyude

rust/kernel/sync/lock.rs

@@ -234,7 +234,7 @@ impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> {
     /// # Safety
     ///
     /// The caller must ensure that it owns the lock.
-    pub(crate) unsafe fn new(lock: &'a Lock<T, B>, state: B::GuardState) -> Self {
+    pub unsafe fn new(lock: &'a Lock<T, B>, state: B::GuardState) -> Self {
         Self {
             lock,
             state,