rust: gpu: Add GPU buddy allocator bindings

rust: gpu: Add GPU buddy allocator bindings

Add safe Rust abstractions over the Linux kernel's GPU buddy
allocator for physical memory management. The GPU buddy allocator
implements a binary buddy system useful for GPU physical memory
allocation. nova-core will use it for physical memory allocation.

Cc: Nikola Djukic <ndjukic@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260320045711.43494-2-joelagnelf@nvidia.com
[ * Use doc-comments for GpuBuddyAllocMode methods and GpuBuddyGuard,
  * Fix comma splice in GpuBuddyParams::chunk_size doc-comment,
  * Remove redundant summary in GpuBuddy::new doc-comment,
  * Drop Rust helper for gpu_buddy_block_size().

    - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>