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