rust: dma: implement DataDirection

rust: dma: implement DataDirection

Add the `DataDirection` struct, a newtype wrapper around the C
`enum dma_data_direction`.

This provides a type-safe Rust interface for specifying the direction of
DMA transfers.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://lore.kernel.org/r/20250828133323.53311-2-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>