rust: Enable the new_uninit feature for kernel and driver crates

The unstable new_uninit feature enables various library APIs to create
uninitialized containers, such as `Box::assume_init()`. This is
necessary to build abstractions that directly initialize memory at the
target location, instead of doing copies through the stack.

Will be used by the DRM scheduler abstraction in the kernel crate, and
by field-wise initialization (e.g. using `place!()` or a future
replacement macro which may itself live in `kernel`) in driver crates.

Link: https://github.com/Rust-for-Linux/linux/issues/879
Link: https://github.com/Rust-for-Linux/linux/issues/2
Link: https://github.com/rust-lang/rust/issues/63291


Signed-off-by: Asahi Lina <lina@asahilina.net>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Link: https://lore.kernel.org/r/20230224-rust-new_uninit-v1-1-c951443d9e26@asahilina.net


[ Reworded to use `Link` tags. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>