[ARM] mm: add memory type for inner-writeback

[ARM] mm: add memory type for inner-writeback

For streaming-style operations (e.g., software rendering of graphics
surfaces shared with non-coherent DMA devices), the cost of performing
L2 cache maintenance can exceed the benefit of having the larger cache
(this is particularly true for OUTER_CACHE configurations like the ARM
PL2x0).

This change uses the currently-unused mapping 5 (TEX[0]=1, C=0, B=1)
in the tex remapping tables as an inner-writeback-write-allocate, outer
non-cacheable memory type, so that this mapping will be available to
clients which will benefit from the reduced L2 maintenance.

Change-Id: Iaec3314a304eab2215100d991b1e880b676ac906
Signed-off-by: Gary King <gking@nvidia.com>