Add comments to explain the ilk pipe csc operation a bit better.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190718145053.25808-11-ville.syrjala@linux.intel.comReviewed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>