gpu: nova-core: require `Send` on `FalconEngine` and `FalconHal`

gpu: nova-core: require `Send` on `FalconEngine` and `FalconHal`

We want to store the GSP and SEC2 falcon instances inside the `Gpu`
structure, but doing so require these types to implement `Send` for
`pci::Driver` to remain implementable on `NovaCore`, which embeds `Gpu`.

All implementors of `FalconEngine` and `FalconHal` satisfy the
requirements of `Send`, and these traits also already required `Sync`,
so this a minor tweak.

Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20250913-nova_firmware-v6-1-9007079548b0@nvidia.com
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>