drm/amd/powerplay: notify smu with active display count

when dc update clocks via smu, smu needs to know how many
displays active. this interface is for dc notify number
of active displays to smu.

Signed-off-by: hersen wu <hersenxs.wu@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>