drm/msm: stop abusing dma_map/unmap for cache

Recently splats like this started showing up:

   WARNING: CPU: 4 PID: 251 at drivers/iommu/dma-iommu.c:451 __iommu_dma_unmap+0xb8/0xc0
   Modules linked in: ath10k_snoc ath10k_core fuse msm ath mac80211 uvcvideo cfg80211 videobuf2_vmalloc videobuf2_memops vide
   CPU: 4 PID: 251 Comm: kworker/u16:4 Tainted: G        W         5.2.0-rc5-next-20190619+ #2317
   Hardware name: LENOVO 81JL/LNVNB161216, BIOS 9UCN23WW(V1.06) 10/25/2018
   Workqueue: msm msm_gem_free_work [msm]
   pstate: 80c00005 (Nzcv daif +PAN +UAO)
   pc : __iommu_dma_unmap+0xb8/0xc0
   lr : __iommu_dma_unmap+0x54/0xc0
   sp : ffff0000119abce0
   x29: ffff0000119abce0 x28: 0000000000000000
   x27: ffff8001f9946648 x26: ffff8001ec271068
   x25: 0000000000000000 x24: ffff8001ea3580a8
   x23: ffff8001f95ba010 x22: ffff80018e83ba88
   x21: ffff8001e548f000 x20: fffffffffffff000
   x19: 0000000000001000 x18: 00000000c00001fe
   x17: 0000000000000000 x16: 0000000000000000
   x15: ffff000015b70068 x14: 0000000000000005
   x13: 0003142cc1be1768 x12: 0000000000000001
   x11: ffff8001f6de9100 x10: 0000000000000009
   x9 : ffff000015b78000 x8 : 0000000000000000
   x7 : 0000000000000001 x6 : fffffffffffff000
   x5 : 0000000000000fff x4 : ffff00001065dbc8
   x3 : 000000000000000d x2 : 0000000000001000
   x1 : fffffffffffff000 x0 : 0000000000000000
   Call trace:
    __iommu_dma_unmap+0xb8/0xc0
    iommu_dma_unmap_sg+0x98/0xb8
    put_pages+0x5c/0xf0 [msm]
    msm_gem_free_work+0x10c/0x150 [msm]
    process_one_work+0x1e0/0x330
    worker_thread+0x40/0x438
    kthread+0x12c/0x130
    ret_from_fork+0x10/0x18
   ---[ end trace afc0dc5ab81a06bf ]---

Not quite sure what triggered that, but we really shouldn't be abusing
dma_{map,unmap}_sg() for cache maint.

Cc: Stephen Boyd <sboyd@kernel.org>
Tested-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190630124735.27786-1-robdclark@gmail.com