ARM: Add workaround for Cortex-A9 errata 794072

A short loop including a DMB instruction might cause a denial of
service on another processor which executes a CP15 broadcast operation.
Exists on r1, r2, r3, r4 revisions.

Signed-off-by: Nitin Garg <nitin.garg@freescale.com>
Acked-by: Dirk Behme <dirk.behme@de.bosch.com>