drm/i915/pch: convert intel_pch_display.[ch] to struct intel_display

Going forward, struct intel_display is the main display device data
pointer. Convert as much as possible of intel_pch_display.[ch] to struct
intel_display.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/0341f0c14a4770cfd41708200cd6c5416b8a17b9.1742554320.git.jani.nikula@intel.com


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