drm/amdgpu/vcn: remove JPEG related code from idle handler and begin use

For VCN2.0 and above, VCN has been separated from JPEG

Signed-off-by: Leo Liu <leo.liu@amd.com>
Reviewed-by: James Zhu <James.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>