iommu: msm: Enable Context caching for MMU-500

MMU-500 implements context caching in TLBs and prefetch
buffers of IOMMU. Enabling them would boost performance.
But this implementation is different from what present
SMMU driver expects. So, configure auxiliary registers
for MMU-500.

Change-Id: Ife23428315ccec01cf40d4d2409b3640a38c20bb
Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>