drm/i915: Clear wedged status upon resume

drm/i915: Clear wedged status upon resume

When we wake up from suspend, the device has been powered down and
should come back afresh. We should be able to safely remove the wedged
status from the previous session and start afresh.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170826110935.10237-2-chris@chris-wilson.co.uk
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>