drm/amdgpu: move PT validation back into VM code v2

Saves a bunch of CPU cycles when swapping things back in and
allows us to split the VM headers into a separate file.

v2: rename parameters

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>