drm/i915/gen5+, pch: Enable hotplug detection early

To be consistent with the recent change to enable hotplug detection
early on GEN9 platforms do the same on all non-GMCH platforms starting
from GEN5. On GMCH platforms enabling detection without interrupts isn't
trivial, since AUX and HPD have a shared interrupt line. It could be
done there too by using a SW interrupt mask, but I punt on that for now.

Cc: Shashank Sharma <shashank.sharma@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1485509961-9010-5-git-send-email-imre.deak@intel.com