drm/amdgpu: only set DPM_FLAG_NEVER_SKIP for legacy ATPX BOCO

We only need to set DPM_FLAG_NEVER_SKIP for the legacy ATPX
BOCO case.  D3cold and BACO work as expected.

Acked-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>