Architectures with instrumented (KASAN/KCSAN) atomic operations
natively provide arch_atomic_ variants that are not instrumented.

It turns out that some generic code also requires arch_atomic_ in
order to avoid instrumentation, so provide the arch_atomic_ interface
as a direct map into the regular atomic_ interface for
non-instrumented architectures.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>