drm/i915: Rename intel_load_plane_csc_black()

drm/i915: Rename intel_load_plane_csc_black()

intel_load_plane_csc_black() is specific to icl+ so deserves
a name reflecting that fact. Also rename the variables to
standard form so I won't get confused reading the code.

v2: icl+ not glk+

Cc: Anshuman Gupta <anshuman.gupta@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Juston Li <juston.li@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211006235704.28894-5-ville.syrjala@linux.intel.com
Reviewed-by: Juston Li <juston.li@intel.com>