drm/amd/display: Respect PP_STUTTER_MODE but don't override DC_DISABLE_STUTTER

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>