drm/amdgpu: signal fences directly in amdgpu_fence_process

Because of the scheduler we need to signal all fences immediately
anyway, so try to avoid the waitqueue overhead.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>