iommu: msm: Re-enable Context caching for MMU-500

Original intent:

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.

Reason for re-enable:

Context caching was reverted due to strange issues of
Permission faults at SMMU when this was enabled. Now,
that issue is fixed. Re-enable this feature for
performance needs.

Change-Id: I63829358e501d4c6f7526d5b59a31ab23b1cd0d8
Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>