drm/amdgpu: Wait for reset on init completion

When reset on initialization is requested, wait for the reset to finish.
In cases where module is loaded after boot, this makes sure all
initialization work is done after a successful return of modprobe.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Ramesh Errabolu <ramesh.errabolu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>