drm/i915: Refer to GGTT {,VM} consistently

Refer to the GGTT VM consistently as "ggtt->base" instead of just "ggtt",
"vm" or indirectly through other variables like "dev_priv->ggtt.base"
to avoid confusion with the i915_ggtt object itself and PPGTT VMs.

Refer to the GGTT as "ggtt" instead of indirectly through chaining.

As a bonus gets rid of the long-standing i915_obj_to_ggtt vs.
i915_gem_obj_to_ggtt conflict, due to removal of i915_obj_to_ggtt!

v2:
- Added some more after grepping sources with Chris

v3:
- Refer to GGTT VM through ggtt->base consistently instead of ggtt_vm
  (Chris)

v4:
- Convert all dev_priv->ggtt->foo accesses to ggtt->foo.

v5:
- Make patch checker happy

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index d301173..a66ce49 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -527,6 +527,7 @@
 {
 	struct apertures_struct *ap;
 	struct pci_dev *pdev = dev_priv->dev->pdev;
+	struct i915_ggtt *ggtt = &dev_priv->ggtt;
 	bool primary;
 	int ret;
 
@@ -534,8 +535,8 @@
 	if (!ap)
 		return -ENOMEM;
 
-	ap->ranges[0].base = dev_priv->ggtt.mappable_base;
-	ap->ranges[0].size = dev_priv->ggtt.mappable_end;
+	ap->ranges[0].base = ggtt->mappable_base;
+	ap->ranges[0].size = ggtt->mappable_end;
 
 	primary =
 		pdev->resource[PCI_ROM_RESOURCE].flags & IORESOURCE_ROM_SHADOW;
@@ -1170,6 +1171,7 @@
 static int i915_driver_init_hw(struct drm_i915_private *dev_priv)
 {
 	struct drm_device *dev = dev_priv->dev;
+	struct i915_ggtt *ggtt = &dev_priv->ggtt;
 	uint32_t aperture_size;
 	int ret;
 
@@ -1213,17 +1215,17 @@
 	if (IS_BROADWATER(dev) || IS_CRESTLINE(dev))
 		dma_set_coherent_mask(&dev->pdev->dev, DMA_BIT_MASK(32));
 
-	aperture_size = dev_priv->ggtt.mappable_end;
+	aperture_size = ggtt->mappable_end;
 
-	dev_priv->ggtt.mappable =
-		io_mapping_create_wc(dev_priv->ggtt.mappable_base,
+	ggtt->mappable =
+		io_mapping_create_wc(ggtt->mappable_base,
 				     aperture_size);
-	if (dev_priv->ggtt.mappable == NULL) {
+	if (!ggtt->mappable) {
 		ret = -EIO;
 		goto out_ggtt;
 	}
 
-	dev_priv->ggtt.mtrr = arch_phys_wc_add(dev_priv->ggtt.mappable_base,
+	ggtt->mtrr = arch_phys_wc_add(ggtt->mappable_base,
 					      aperture_size);
 
 	pm_qos_add_request(&dev_priv->pm_qos, PM_QOS_CPU_DMA_LATENCY,
@@ -1266,13 +1268,14 @@
 static void i915_driver_cleanup_hw(struct drm_i915_private *dev_priv)
 {
 	struct drm_device *dev = dev_priv->dev;
+	struct i915_ggtt *ggtt = &dev_priv->ggtt;
 
 	if (dev->pdev->msi_enabled)
 		pci_disable_msi(dev->pdev);
 
 	pm_qos_remove_request(&dev_priv->pm_qos);
-	arch_phys_wc_del(dev_priv->ggtt.mtrr);
-	io_mapping_free(dev_priv->ggtt.mappable);
+	arch_phys_wc_del(ggtt->mtrr);
+	io_mapping_free(ggtt->mappable);
 	i915_ggtt_cleanup_hw(dev);
 }