rust_binder: use KVVec for files_to_translate

The num_fds value in a binder_fd_array_object is bounded by the
transaction buffer. However, its in-kernel metadata is larger than the
u32 array on the wire.

On 64-bit systems, FileEntry occupies 24 bytes. About 900,000 entries
therefore make files_to_translate request roughly 20.6 MiB of
physically contiguous memory, triggering a warning in
__alloc_frozen_pages_noprof.

translate_fds() later allocates Reservation entries from the same
count. At 16 bytes per entry, this requires another 13.7 MiB contiguous
allocation.

Neither vector requires physical contiguity. Use KVVec for both so
large allocations can fall back to vmalloc.

Tested under QEMU/KVM. The 900,000-entry reproducer no longer triggers
a page allocator warning, and a 300,000-entry transaction that repeats
one valid fd reaches translate_fds() without WARN or BUG.

Found with the rust-in-peace agentic pipeline
(https://github.com/scadastrangelove/rust-in-peace).

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Sergey Gordeychik <scadastrangelove@gmail.com>
Link: https://patch.msgid.link/20260828090757.96282-1-scadastrangelove@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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