drm/amdgpu: enable huge page handling in the VM v5

The hardware can use huge pages to map 2MB of address space with only one PDE.

v2: few cleanups and rebased
v3: skip PT updates if we are using the PDE
v4: rebased, added support for CPU based updates
v5: fix CPU based updates once more
v6: fix ndw estimation

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-and-tested-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>