rust: lock: Pin the inner data

rust: lock: Pin the inner data

In preparation to support Lock<T> where T is pinned, the first thing
that needs to be done is to structurally pin the 'data' member. This
switches the 't' parameter in Lock<T>::new() to take in an impl
PinInit<T> instead of a plain T. This in turn uses the blanket
implementation "impl PinInit<T> for T".

Subsequent patches will touch on Guard<T>.

Suggested-by: Benno Lossin <lossin@kernel.org>
Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://github.com/Rust-for-Linux/linux/issues/1181