drm/amd/display: Set chroma taps to 1 if luma taps are 1

drm/amd/display: Set chroma taps to 1 if luma taps are 1

When luma is unscaled we also want chroma to be pixel-perfect.
When luma taps are > 1 the result will be a blurred luma plane,
even when the image isn't scaled.

This makes IGT tests for CSC colorop pass.

Assisted-by: Claude: claude-sonnet-4.5
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>