drm/amd/powerplay: hwmon don't check powerplay when sw smu is enabled

when sw-smu is enabled, the driver won't init powerplay structure.

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