drm/amdgpu/vcn: not pause dpg for unified queue

For unified queue, DPG pause for encoding is done inside VCN firmware,
so there is no need to pause dpg based on ring type in kernel.

For VCN3 and below, pausing DPG for encoding in kernel is still needed.

v2: add more comments
v3: update commit message

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Ruijing Dong <ruijing.dong@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>