drm/i915/display: include intel_display_reg_defs.h from display regs files

Some display register files include i915_reg_defs.h, some don't include
anything. Prefer intel_display_reg_defs.h in display.

Reviewed-by: Michał Grzelak <michal.grzelak@intel.com>
Link: https://lore.kernel.org/r/06c24e1f6a7a2f6b4801b0a079eec3cc924402a7.1749469962.git.jani.nikula@intel.com


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