drm/amd/display: Always Scale Flag

[Why & How]
When always scale flag is set at the API level, the number of taps
should not be overridden to zero in the identity scaling ratio case,
and luma scale should not be set to bypass regardless of luma scale
ratio

Reviewed-by: Samson Tam <samson.tam@amd.com>
Signed-off-by: Jesse Agate <jesse.agate@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>