drm/amdgpu: add vcn jpeg sw finish

Add software finish for vcn jpeg ring.

v2: remove unnecessary scheduler entity.

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>