drm/i915: less magic for stolen preallocated objects w/o gtt offset

A magic -1 is a obscure, especially since it's actually passed as an
unsigned, so depends upon the magic sign extension rules in C. This has
been added in

commit 3727d55e4d85836aa6cb759a965daaef88074150
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Wed May 8 10:45:14 2013 -0700

    drm/i915: allow stolen, pre-allocated objects to avoid GTT allocation v2

Use a proper #define instead. Spotted while reviewing Ben's
drm_mm_create_block changes.

v2: Cast the constant to u32 since otherwise we again have a type
mismatch. Suggested by Chris Wilson.

Cc: Ben Widawsky <ben@bwidawsk.net>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1202,6 +1202,7 @@ enum hdmi_force_audio {
 };
 
 #define I915_GTT_RESERVED ((struct drm_mm_node *)0x1)
+#define I915_GTT_OFFSET_NONE ((u32)-1)
 
 struct drm_i915_gem_object_ops {
 	/* Interface between the GEM object and its backing storage.

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -360,7 +360,7 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev,
 	}
 
 	/* Some objects just need physical mem from stolen space */
-	if (gtt_offset == -1)
+	if (gtt_offset == I915_GTT_OFFSET_NONE)
 		return obj;
 
 	/* To simplify the initialisation sequence between KMS and GTT,

drivers/gpu/drm/i915/intel_pm.c

@@ -3474,7 +3474,7 @@ static void valleyview_setup_pctx(struct drm_device *dev)
 		pcbr_offset = (pcbr & (~4095)) - dev_priv->mm.stolen_base;
 		pctx = i915_gem_object_create_stolen_for_preallocated(dev_priv->dev,
 								      pcbr_offset,
-								      -1,
+								      I915_GTT_OFFSET_NONE,
 								      pctx_size);
 		goto out;
 	}