drm/msm/a6xx: Add support for using system cache(LLC)

The last level system cache can be partitioned to 32 different
slices of which GPU has two slices preallocated. One slice is
used for caching GPU buffers and the other slice is used for
caching the GPU SMMU pagetables. This talks to the core system
cache driver to acquire the slice handles, configure the SCID's
to those slices and activates and deactivates the slices upon
GPU power collapse and restore.

Some support from the IOMMU driver is also needed to make use
of the system cache to set the right TCR attributes. GPU then
has the ability to override a few cacheability parameters which
it does to override write-allocate to write-no-allocate as the
GPU hardware does not benefit much from it.

DOMAIN_ATTR_IO_PGTABLE_CFG is another domain level attribute used
by the IOMMU driver for pagetable configuration which will be used
to set a quirk initially to set the right attributes to cache the
hardware pagetables into the system cache.

Signed-off-by: Sharat Masetty <smasetty@codeaurora.org>
[saiprakash.ranjan: fix to set attr before device attach to iommu and rebase]
Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>