rust: add `pin-init` as a dependency to `bindings` and `uapi`

rust: add `pin-init` as a dependency to `bindings` and `uapi`

This allows `bindings` and `uapi` to implement `Zeroable` and use other
items from pin-init.

Co-developed-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://rust-for-linux.zulipchat.com/#narrow/channel/291565-Help/topic/Zeroable.20trait.20for.20C.20structs/near/510264158
Signed-off-by: Benno Lossin <lossin@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>