arm64: cmpxchg: patch in lse instructions when supported by the CPU

On CPUs which support the LSE atomic instructions introduced in ARMv8.1,
it makes sense to use them in preference to ll/sc sequences.

This patch introduces runtime patching of our cmpxchg primitives so that
the LSE cas instruction is used instead.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --cc arch/arm64/include/asm/atomic.h
Simple merge

diff --cc arch/arm64/include/asm/atomic_ll_sc.h
Simple merge

diff --cc arch/arm64/include/asm/atomic_lse.h
Simple merge

diff --cc arch/arm64/include/asm/cmpxchg.h
Simple merge