drm/amdgpu/vcn: enable indirect DPG SRAM mode for navi14

Enable VCN dynamic powergating for navi14.

Signed-off-by: Xiaojie Yuan <xiaojie.yuan@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>