drm/i915/scaler: Limit pipe scaler downscaling factors for YUV420

Limit downscaling to less than 1.5 (source/destination) in
the horizontal direction and 1.0 in the vertical direction,
When configured for Pipe YUV 420 encoding for port output.

Bspec: 50441, 7490, 69901
Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250120172209.188488-6-mitulkumar.ajitkumar.golani@intel.com