drm/i915: split out display register macros to a separate file

This is a scripted split of the display related register macros from
i915_reg.h to display/intel_display_regs.h. As a starting point, move
all the macros that are only used in display code (or GVT). If there are
users in core i915 code or soc/, or no users anywhere, keep the macros
in i915_reg.h. This is done in groups of macros separated by blank
lines, moving the comments along with the groups.

Some manually picked macro groups are kept/moved regardless of the
heuristics above.

This is obviously a very crude approach. It's not perfect. But there are
4.2k lines in i915_reg.h, and its refactoring has ground to a halt. This
is the big hammer that splits the file to two, and enables further
cleanup.

Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com> # v2
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20250606102256.2080073-1-jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>