drm/amd/powerplay: implement sysfs of pp_cur_state function

add function of smu_get_currente_state for sw-smu.

v2: fix code typo error if (ret);

Signed-off-by: Kevin Wang <Kevin1.Wang@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>