This option enables the workaround for the 742230 Cortex-A9
(r1p0..r2p2) erratum. Under rare circumstances, a DMB instruction
between two write operations may not ensure the correct visibility
ordering of the two writes. This workaround sets a specific bit in
the diagnostic register of the Cortex-A9 which causes the DMB
instruction to behave as a DSB, ensuring the correct behaviour of
the two writes.