drm/i915/casf: Handle CASF in skl_scaler_get_filter_select()

drm/i915/casf: Handle CASF in skl_scaler_get_filter_select()

Nuke the duplicate CASF_SCALER_FILTER_SELECT and just have
skl_scaler_get_filter_select() return the proper value for
sharpness filter use. It is the same "use programmable coefficients"
value we already use for the nearest neighbor filtering.

Reviewed-by: Michał Grzelak <michal.grzelak@intel.com>
Reviewed-by: Nemesa Garg <nemesa.garg@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260407175244.19654-6-ville.syrjala@linux.intel.com