rust: Fix build break because of "download-rustc" and "llvm-tools"

rust: Fix build break because of "download-rustc" and "llvm-tools"

>From Rust 1.84, the download-rustc and llvm-tools options were set to True
(previously they were False)

https://github.com/rust-lang/rust/commit/cce6f03754f096f8a2bdfb357e3739b855e29366
(download-rustc)

https://github.com/rust-lang/rust/commit/38f0c099b2e684ea689633eb424d8737a1063a5e
(llvm-tools)

For tarball sources, the download-rustc option should be False, so it has been
reverted back to False.

Setting llvm-tools to True caused issues with finding llvm-objcopy, so this
has been changed back to False.

Upstream-Status: https://github.com/rust-lang/rust/pull/134240/

Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>