drm/amd/powerplay: debugfs don't check powerplay when SW SMU is enabled.

when sw smu is enabled, the powerplay interface isn't implemented.

Signed-off-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>