drm/i915: group display-related register calls

intel_gt_driver_register() may be called earlier than
intel_opregion_register() and acpi_video_register(), so move it up.

intel_display_debugfs_register() may be called later, together with the
other display-related initializations. There is a slight change in
behavior that sysfs files will show up before the display-related
debugfs files, but that shouldn't be a problem - userspace shouldn't be
relying in debugfs.

This allows us to group all the display-related calls under a single
check for "HAS_DISPLAY()" that can be later moved to a better place.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20210213042756.953007-2-lucas.demarchi@intel.com