drm/amdgpu: save VCN instances init info before jpeg init

JPEG init header will overwirte vcn init header info which will loss
some debug information

Signed-off-by: Lin.Cao <lincao12@amd.com>
Reviewed-by: Jingwen Chen <Jingwen.Chen2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>