drm/i915/hotplug: refactor hotplug init slightly

Rename intel_hpd_init_work() to the more generic intel_hpd_init_early(),
and move the hotplug storm initialization there. This lets us move the
HPD_STORM_DEFAULT_THRESHOLD macro to intel_hotplug.c too.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220916130634.3781122-2-jani.nikula@intel.com