drm/amdgpu: move apu flags initialization to the start of device init

In some asics, we need to adjust the behavior according to the apu flags
at very early stage.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Aaron Liu <aaron.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>