drm/i915/display: convert some intel_display.[ch] functions to struct intel_display

drm/i915/display: convert some intel_display.[ch] functions to struct intel_display

Going forward, struct intel_display is the main display device data
pointer. The intel_display.[ch] files are too big to convert in one
go. Convert the interface towards intel_display_driver.c to struct
intel_display.

Reviewed-by: Nemesa Garg <nemesa.garg@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ee8b108420763cbf47ee77fa35b782a7293f9cfe.1741084010.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>