iommu/io-pgtable-fast: Configure to use outer shareable

Change over to using outer shareable for both coherent and
non-coherent page tables and for both coherent and non-coherent
data buffers.
This is done to be more in line with the ARM spec.

Change-Id: I9d85359e9f558a1332670a7eebc53e72a0c06526
Signed-off-by: Liam Mark <lmark@codeaurora.org>