drm/amdgpu: implement soft_recovery for GFX8 v2

Try to kill waves on the SQ.

v2: only for the GFX ring for now.

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