rust: dma: add `Send` implementation for `CoherentAllocation`

Stephen found a future build failure in linux-next [1]:

error[E0277]: `*mut MyStruct` cannot be sent between threads safely
-

rust: dma: add `Send` implementation for `CoherentAllocation`

Stephen found a future build failure in linux-next [1]:

error[E0277]: `*mut MyStruct` cannot be sent between threads safely
--> samples/rust/rust_dma.rs:47:22
|
47 | impl pci::Driver for DmaSampleDriver {
| ^^^^^^^^^^^^^^^ `*mut MyStruct` cannot be sent between threads safely

It is caused by the interaction between commit 935e1d90bf6f ("rust: pci:
require Send for Driver trait implementers") from the driver-core tree,
which fixes a missing concurrency requirement, and commit 9901addae63b
("samples: rust: add Rust dma test sample driver") which adds a sample
that does not satisfy that requirement.

Add a `Send` implementation to `CoherentAllocation`, which allows the
sample (and other future users) to satisfy it.

Reported-by: Stephen Rothwell <[email protected]>
Closes: https://lore.kernel.org/linux-next/[email protected]/ [1]
Signed-off-by: Danilo Krummrich <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Added number to Closes. Fix typo spotted by Boqun. - Miguel ]
Signed-off-by: Miguel Ojeda <[email protected]>

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rust: add dma coherent allocator abstraction

Add a simple dma coherent allocator rust abstraction. Based on
Andreas Hindborg's dma abstractions from the rnvme driver, which
was also based on earlier

rust: add dma coherent allocator abstraction

Add a simple dma coherent allocator rust abstraction. Based on
Andreas Hindborg's dma abstractions from the rnvme driver, which
was also based on earlier work by Wedson Almeida Filho.

Reviewed-by: Alice Ryhl <[email protected]>
Signed-off-by: Abdiel Janulgue <[email protected]>
Acked-by: Danilo Krummrich <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Nacked-by: Christoph Hellwig <[email protected]>
[ Removed period. - Miguel ]
Signed-off-by: Miguel Ojeda <[email protected]>

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