drm/amdgpu: re-apply "use the new cursor in the VM code" v2

Now that we found the underlying problem we can re-apply this patch.

This reverts commit 6b44b667

.

v2: rebase on KFD changes

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Tested-by: Nirmoy Das <nirmoy.das@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>