drm/amd/display: making DCN20 WM table non-overlapping

[why]
Existing behavior has overlapping ranges resulting in path
dependent SMU selection

[how]
Make ranges non-overlapping, resulting in non-path dependent
selection

Signed-off-by: Jun Lei <Jun.Lei@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>