drm/i915: Enable hotplug interrupts after querying hw capabilities.

drm/i915: Enable hotplug interrupts after querying hw capabilities.

sdvo->hotplug_active is initialised during intel_sdvo_setup_outputs(),
and so we never enabled the hotplug interrupts on SDVO as we were
checking too early.

This regression has been introduced somewhere in the hpd rework for
the storm detection and handling starting with

commit 1d843f9de4e6dc6a899b6f07f106c00da09925e6
Author: Egbert Eich <eich@suse.de>
Date:   Mon Feb 25 12:06:49 2013 -0500

    DRM/I915: Add enum hpd_pin to intel_encoder.

and the follow-up patches to use the new encoder->hpd_pin variable for
the different irq setup functions.

The problem is that encoder->hpd_pin was set up _before_ the output
setup was done and so before we could assess the hotplug capabilities
of the outputs on an sdvo encoder.

Reported-by: Alex Fiestas <afiestas@kde.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=58405
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
[danvet: Add regression note.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>