drm/amd/display: Move ntuple to insert entry

Move get_optimal_ntuple to the FPU code and call it inside
insert_entry_into_table_sorted.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>