drm/amdgpu: flip frag_ptes and update_pts

We can add the fragment params before we split the update for the page tables.
That should save a few CPU cycles for larger updates.

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