HW coherency won't work properly for CAAM write transactions
if AWCACHE is left to default (POR) value - 4'b0001.
It has to be programmed to 4'b0010, i.e. AXI3 Cacheable bit set.

For platforms that have HW coherency support:
-PPC-based: the update has no effect; CAAM coherency already works
due to the IOMMU (PAMU) driver setting the correct memory coherency
attributes
-ARM-based: the update fixes cache coherency issues,
since IOMMU (SMMU) driver is not programmed to behave similar to PAMU

Signed-off-by: Horia Geant? <horia.geanta@freescale.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>