drm/intel/display: Add support for pipe background color (v4)

drm/intel/display: Add support for pipe background color (v4)

Gen9 platforms allow CRTC's to be programmed with a background/canvas
color below the programmable planes.  Let's expose this as a property to
allow userspace to program a desired value.

This patch is based on earlier work by Chandra Konduru and Matt Roper.
Between 2018 and now, intel/display has changed so much that another
rewrite was necessary.

v2:
 - Set initial background color (black) via proper helper function (Bob)
 - Fix debugfs output
 - General rebasing
v3 (Maarten):
 - Rebase on top of recent changes.
v4 (Maarten):
 - Complete rewrite based on the solution that went upstream, and
   on the new intel color management features.

Cc: Chandra Konduru <chandra.konduru@intel.com>
Cc: dri-devel@lists.freedesktop.org
Co-developed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
Link: https://patch.msgid.link/20260505200133.636584-2-dev@lankhorst.se
Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>