FROMLIST: arm64: rust: Enable Rust support for AArch64

This commit provides the build flags for Rust for AArch64. The core Rust
support already in the kernel does the rest. This enables the PAC ret
and BTI options in the Rust build flags to match the options that are
used when building C.

The Rust samples have been tested with this commit.

Bug: 308623796
Change-Id: I582e33974ff3db33aa3b331275137d6ce6a87556
Signed-off-by: Jamie Cunliffe <Jamie.Cunliffe@arm.com>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20231020155056.3495121-3-Jamie.Cunliffe@arm.com


[boqun: Resolve conflicts against loongarch]
Signed-off-by: Matthew Maurer <mmaurer@google.com>