drm/i915: Re-enable the command parser when using PPGTT

In commit

commit 896ab1a5
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed Aug 6 15:04:51 2014 +0200

    drm/i915: Fix up checks for aliasing ppgtt

it looks like we accidentally inverted the check that the command
parser should only run when the driver enables some form of PPGTT.

Testcase: igt/gem_exec_parse
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Brad Volkin <bradley.d.volkin@intel.com>
[danvet: Also drop the comment right above, all production vlv now
have hw ppgtt enabled.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_cmd_parser.c

@@ -845,12 +845,7 @@ bool i915_needs_cmd_parser(struct intel_engine_cs *ring)
 	if (!ring->needs_cmd_parser)
 		return false;
 
-	/*
-	 * XXX: VLV is Gen7 and therefore has cmd_tables, but has PPGTT
-	 * disabled. That will cause all of the parser's PPGTT checks to
-	 * fail. For now, disable parsing when PPGTT is off.
-	 */
-	if (USES_PPGTT(ring->dev))
+	if (!USES_PPGTT(ring->dev))
 		return false;
 
 	return (i915.enable_cmd_parser == 1);