drm/amd/display: adding pathway to retrieve stutter period

why:
some functions may need be dependent on stutter period in the future

how:
Extract from stutter calculations and place into perf_params structure

Signed-off-by: Martin Leung <martin.leung@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>