Hardware status page needs to have proper seqno set
as our initial seqno can be arbitrary. If initial seqno is close
to wrap boundary on init and i915_seqno_passed() (31bit space)
refers to hw status page which contains zero, errorneous result
will be returned.

v2: clear mboxes and set hws page directly instead of going
through rings. Suggested by Chris Wilson.

v3: hws needs to be updated for all gens. Noticed by Chris
Wilson.

References: https://bugs.freedesktop.org/show_bug.cgi?id=58230Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>