drm/i915/opregion: Register display debugfs later, after initialization steps

Move the display debugfs registration later, after initializing steps
for opregion/acpi/audio. These latter ones don't depend on the debugfs
entries, OTOH some debugfs entries may depend on the initialized state.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230308162503.3219200-3-imre.deak@intel.com