If the device does not support the aliasing ppgtt, we must translate
user bind requests (PIN_USER) from LOCAL_BIND to a GLOBAL_BIND. However,
since this is device specific we cannot do this conveniently in the
upper layers and so must manage the vma->bound flags in the backend.

Partial revert of commit 75d04a37 [4.2-rc1]
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

Note this was spotted by Daniel originally, but we dropped the ball in
getting the fix in before the bug going wild. Sorry all.

Reported-by: Vincent Legoll vincent.legoll@gmail.com
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91133
References: https://bugs.freedesktop.org/show_bug.cgi?id=90224Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>