DRM/i915: Convert HPD interrupts to make use of HPD pin assignment in encoders (v2)

This allows to enable HPD interrupts for individual pins to only receive
hotplug events from lines which are connected and working.

v2: Restructured initailization of const arrays following a suggstion
    by Chris Wilson <chris@chris-wilson.co.uk>

Signed-off-by: Egbert Eich <eich@suse.de>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org> (v1)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>