drm/i915: Don't mark pdps clear if pdps are not submitted

Don't mark pdps clear if never do the necessary actions
with the hardware to make them clear.

v2: totally get rid of confusing ppgtt bool (Chris)

Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1488295691-9404-2-git-send-email-mika.kuoppala@intel.com