drm/i915/display: move hotplug.dp_wq init from xe and i915 to display

The workqueue init and destroy belongs in display. Move it.

Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://lore.kernel.org/r/4730167548a40dc2abe38cd084809b74de988f1a.1747397638.git.jani.nikula@intel.com


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