gpu: ion: Return an integer for ion_unmap_iommu()

Need this for my future mdp hacks.

Signed-off-by: Sultanxda <sultanxda@gmail.com>
mdp4_overlay: Conditionally call ion_unmap_iommu()

Don't call ion_unmap_iommu() if iommu was never mapped.

[ 3064.936981] WARNING: at drivers/gpu/ion/ion.c:750 ion_unmap_iommu+0xb8/0xe0()
[ 3064.937683] ion_unmap_iommu: (2,2) was never mapped for d5f3af00

Signed-off-by: Sultanxda <sultanxda@gmail.com>
gpu: ion: Don't issue kernel WARNING for iommu_map failure

This isn't serious enough of an error to warrant the use of a kernel WARNING.

Signed-off-by: Sultanxda <sultanxda@gmail.com>