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_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 374a0cb..0ee61fd 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -313,7 +313,8 @@
 		   uint64_t target_offset)
 {
 	struct drm_device *dev = obj->base.dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct drm_i915_private *dev_priv = to_i915(dev);
+	struct i915_ggtt *ggtt = &dev_priv->ggtt;
 	uint64_t delta = relocation_target(reloc, target_offset);
 	uint64_t offset;
 	void __iomem *reloc_page;
@@ -330,7 +331,7 @@
 	/* Map the page containing the relocation we're going to perform.  */
 	offset = i915_gem_obj_ggtt_offset(obj);
 	offset += reloc->offset;
-	reloc_page = io_mapping_map_atomic_wc(dev_priv->ggtt.mappable,
+	reloc_page = io_mapping_map_atomic_wc(ggtt->mappable,
 					      offset & PAGE_MASK);
 	iowrite32(lower_32_bits(delta), reloc_page + offset_in_page(offset));
 
@@ -340,7 +341,7 @@
 		if (offset_in_page(offset) == 0) {
 			io_mapping_unmap_atomic(reloc_page);
 			reloc_page =
-				io_mapping_map_atomic_wc(dev_priv->ggtt.mappable,
+				io_mapping_map_atomic_wc(ggtt->mappable,
 							 offset);
 		}
 
@@ -1431,7 +1432,8 @@
 		       struct drm_i915_gem_execbuffer2 *args,
 		       struct drm_i915_gem_exec_object2 *exec)
 {
-	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct drm_i915_private *dev_priv = to_i915(dev);
+	struct i915_ggtt *ggtt = &dev_priv->ggtt;
 	struct drm_i915_gem_request *req = NULL;
 	struct eb_vmas *eb;
 	struct drm_i915_gem_object *batch_obj;
@@ -1504,7 +1506,7 @@
 	if (ctx->ppgtt)
 		vm = &ctx->ppgtt->base;
 	else
-		vm = &dev_priv->ggtt.base;
+		vm = &ggtt->base;
 
 	memset(&params_master, 0x00, sizeof(params_master));