drm/i915: restore ggtt double-bind avoidance

This was accidentally lost in

commit 75d04a37
Author: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Date:   Tue Apr 28 17:56:17 2015 +0300

    drm/i915/gtt: Allocate va range only if vma is not bound

While at it implement an improved version suggested by Chris which
avoids the double-bind irrespective of what type of bind is done
first.

Note that this exact bug was already addressed in

commit d0e30adc
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Wed Jul 29 20:02:48 2015 +0100

    drm/i915: Mark PIN_USER binding as GLOBAL_BIND without the aliasing ppgtt

but the problem is still that originally in

commit 0875546c


Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Mon Apr 20 09:04:05 2015 -0700

    drm/i915: Fix up the vma aliasing ppgtt binding

if forgotten to take into account there case where we have a
GLOBAL_BIND before a LOCAL_BIND. This patch here fixes that.

v2: Pimp commit message and revert the partial fix.

v3: Split into two functions to specialize on aliasing_ppgtt y/n.

v4: WARN_ON for paranoia in the init sequence, since the ggtt probe
and aliasing ppgtt setup are far apart.

v5: Style nits.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://mid.gmane.org/1444911781-32607-1-git-send-email-daniel.vetter@ffwll.ch
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>