drm/msm/mdp4: stop supporting no-IOMMU configuration

With the switch to GPUVM the msm driver no longer supports the no-IOMMU
configurations (even without the actual GPU). Return an error in case we
face the lack of the IOMMU for an MDP4 device.

Fixes: 111fdd21 ("drm/msm: drm_gpuvm conversion")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/672557/


Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>