gpu: ion: Introduce ion_dynamic_map_iommu() helper function

This function performs ion_map_iommu() but it unmaps iommu first if the requested handle to map to has already been mapped to.

Signed-off-by: Sultanxda <sultanxda@gmail.com>
mdp4_overlay: Use ion_dynamic_map_iommu() for domain 2 & partition 2

This ensures that ion_map_iommu() is always successful for domain 2 & partition 2.

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