rust: cfi: only 64-bit arm and x86 support CFI_CLANG

rust: cfi: only 64-bit arm and x86 support CFI_CLANG

The kernel uses the standard rustc targets for non-x86 targets, and out
of those only 64-bit arm's target has kcfi support enabled. For x86, the
custom 64-bit target enables kcfi.

The HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC config option that allows
CFI_CLANG to be used in combination with RUST does not check whether the
rustc target supports kcfi. This breaks the build on riscv (and
presumably 32-bit arm) when CFI_CLANG and RUST are enabled at the same
time.

Ordinarily, a rustc-option check would be used to detect target support
but unfortunately rustc-option filters out the target for reasons given
in commit 46e24a545cdb4 ("rust: kasan/kbuild: fix missing flags on first
build"). As a result, if the host supports kcfi but the target does not,
e.g. when building for riscv on x86_64, the build would remain broken.

Instead, make HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC depend on the only
two architectures where the target used supports it to fix the build.

CC: stable@vger.kernel.org
Fixes: ca627e636551e ("rust: cfi: add support for CFI_CLANG with Rust")
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250908-distill-lint-1ae78bcf777c@spud
Signed-off-by: Paul Walmsley <pjw@kernel.org>