drm/msm/iommu: optimize map/unmap

Using map_pages/unmap_pages cuts down on the # of pgtable walks needed
in the process of finding where to insert/remove an entry.  The end
result is ~5-10x faster than mapping a single page at a time.

v2: Rename iommu_pgsize(), drop obsolete comments, fix error handling
    in msm_iommu_pagetable_map()

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Sai Prakash Ranjan <quic_saipraka@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/498892/
Link: https://lore.kernel.org/r/20220823163719.90399-1-robdclark@gmail.com