This option enables the workaround for the 754327 Cortex-A9 (prior to
r2p0) erratum. The Store Buffer does not have any automatic draining
mechanism and therefore a livelock may occur if an external agent
continuously polls a memory location waiting to observe an update.
This workaround defines cpu_relax() as smp_mb(), preventing correctly
written polling loops from denying visibility of updates to memory.