We do not use the virtual engines for interrupts (they have physical
components), but we do use them to decouple the fence signaling during
submission. Currently, when we submit a completed request, we try to
enable the interrupt handler for the virtual engine, but we never disarm
it. A quick fix is then to mark the irq as enabled, and it will then
remain enabled -- and this prevents us from waking the device and never
letting it sleep again.

Fixes: f8db4d05 ("drm/i915: Initialise breadcrumb lists on the virtual engine")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: <stable@vger.kernel.org> # v5.5+
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200711203236.12330-1-chris@chris-wilson.co.uk
(cherry picked from commit 4fe6abb8)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>