drm/amd/display: Update idle optimization handling

[How]
 - use dc interface instead of hwss interface in cursor functions, to keep
dc->idle_optimizations_allowed updated
 - add dc interface to check if idle optimizations might apply to a plane

Signed-off-by: Joshua Aberback <joshua.aberback@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>