drm/i915/vlv: re-enable hotplug detect based probing on VLV/BYT

Fixed with

commit 10603caa
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Mon Aug 26 19:51:06 2013 -0300

    drm/i915: Apply the force-detect VGA w/a to Valleyview

Signed-off-by: Jesse Barnes <jbarnes@virtuosugeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>