Rust fixes for v6.12
Toolchain and infrastructure:
- Fix/improve a couple 'depends on' on the newly added CFI/KASAN
suppport to avoid build errors/warnings.
- Fix ARCH_SLAB_MINALIGN multiple definition error for RISC-V under
!CONFIG_MMU.
- Clean upcoming (Rust 1.83.0) Clippy warnings.
'kernel' crate:
- 'sync' module: fix soundness issue by requiring 'T: Sync' for
'LockedBy::access'; and fix helpers build error under PREEMPT_RT.
- Fix trivial sorting issue ('rustfmtcheck') on the v6.12 Rust merge.