drm/amdkfd: Avoid calling amd_iommu_unbind_pasid() when suspending

When kfd suspending on APU, we do not need to call
amd_iommu_unbind_pasid(), because pasid will be unbound automatically
when power goes off.

On the other hand, calling amd_iommu_unbind_pasid() will trigger
kfd_process_iommu_unbind_callback() if the process is not terminating.
By design, kfd_process_iommu_unbind_callback() should only be called
for process terminating. So we would rather not to call
amd_iommu_unbind_pasid() when suspending.

Signed-off-by: Yong Zhao <yong.zhao@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>