drm/amdgpu: Move scheduler init to after XGMI is ready

Before we initialize schedulers we must know which reset
domain are we in - for single device there iis a single
domain per device and so single wq per device. For XGMI
the reset domain spans the entire XGMI hive and so the
reset wq is per hive.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://www.spinics.net/lists/amd-gfx/msg74112.html