drm/i915: Remove i915_address_space.start

Once upon a time, back in the UMS days, we supported userspace
initialising the GTT and sharing portions of the GTT with other users.
Now, we own the GTT (both global and per-process) and the tables always
start at 0 - so we can remove i915_address_space.start and forget about
this old complication.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170215084357.19977-20-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -476,7 +476,7 @@ static int i915_gem_object_info(struct seq_file *m, void *data)
 		   dpy_count, dpy_size);
 
 	seq_printf(m, "%llu [%llu] gtt total\n",
-		   ggtt->base.total, ggtt->mappable_end - ggtt->base.start);
+		   ggtt->base.total, ggtt->mappable_end);
 
 	seq_putc(m, '\n');
 	print_batch_pool_stats(m, dev_priv);