drm/amd/display: enable optional pipe split for single display

also refactor debug option.  now pipe_split_policy are
dynamic = no hack around dcn_calcs.  will split based on HW recommendation
avoid = avoid split if we can support the config with higher voltage
avoid_multi_display = allow split with single display output.

force_single_disp_pipe_split
force single display to pipe split to improve stutter efficiency
by using DET buffers using 2 HUBP.

Signed-off-by: Tony Cheng <tony.cheng@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>