drm/i915: Don't reinit hpd interrupts after gpu reset

Somehow I've overlooked this when simplifying the irq reinit
scheme on gen4.5+ in

commit 78ad455fd229c6f6cc2f390ccbe0d8f1a62d55a9
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Thu May 22 22:18:21 2014 +0200

    drm/i915: Improve irq handling after gpu resets

Since display interrups in general survive a gpu reset on those
platforms there's also no need to reinit the hotplug settings.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>