drm/framebuffer: Format modifier for Intel Gen 12 render compression with Clear Color

Gen12 display can decompress surfaces compressed by render engine with
Clear Color, add a new modifier as the driver needs to know the surface
was compressed by render engine.

V2: Description changes as suggested by Rafael.
V3: Mention the Clear Color size of 64 bits in the comments(DK)
v4: Fix trailing whitespaces
v5: Explain Clear Color in the documentation.
v6: Documentation Nitpicks(Nanley)

Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Kalyan Kondapally <kalyan.kondapally@intel.com>
Cc: Rafael Antognolli <rafael.antognolli@intel.com>
Cc: Nanley Chery <nanley.g.chery@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Nanley Chery <nanley.g.chery@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210114201314.783648-2-imre.deak@intel.com

include/uapi/drm/drm_fourcc.h

@@ -527,6 +527,25 @@ extern "C" {
  */
 #define I915_FORMAT_MOD_Y_TILED_GEN12_MC_CCS fourcc_mod_code(INTEL, 7)
 
+/*
+ * Intel Color Control Surface with Clear Color (CCS) for Gen-12 render
+ * compression.
+ *
+ * The main surface is Y-tiled and is at plane index 0 whereas CCS is linear
+ * and at index 1. The clear color is stored at index 2, and the pitch should
+ * be ignored. The clear color structure is 256 bits. The first 128 bits
+ * represents Raw Clear Color Red, Green, Blue and Alpha color each represented
+ * by 32 bits. The raw clear color is consumed by the 3d engine and generates
+ * the converted clear color of size 64 bits. The first 32 bits store the Lower
+ * Converted Clear Color value and the next 32 bits store the Higher Converted
+ * Clear Color value when applicable. The Converted Clear Color values are
+ * consumed by the DE. The last 64 bits are used to store Color Discard Enable
+ * and Depth Clear Value Valid which are ignored by the DE. A CCS cache line
+ * corresponds to an area of 4x1 tiles in the main surface. The main surface
+ * pitch is required to be a multiple of 4 tile widths.
+ */
+#define I915_FORMAT_MOD_Y_TILED_GEN12_RC_CCS_CC fourcc_mod_code(INTEL, 8)
+
 /*
  * Tiled, NV12MT, grouped in 64 (pixels) x 32 (lines) -sized macroblocks
  *