drm/i915: Remove gtt_mappable_total

With the assertion from the previous patch in place, it should be safe
to get rid gtt_mappable_total. Keeps things saner to not have to track
the same info in two places.

In order to keep the diff as simple as possible and keep with the
existing gtt_setup semantics we opt to keep gtt_mappable_end. It's not
as consistent with the 'total' used in the previous patch, but that can
be fixed later.

Reviewed-by: Rodrigo Vivi <[e-mail]>
[Ben modified commit message]
Signed-off-by: Ben Widawsky <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>

drivers/gpu/drm/i915/i915_debugfs.c

···
 		   count, size);
 
 	seq_printf(m, "%zu [%zu] gtt total\n",
-		   dev_priv->mm.gtt_total, dev_priv->mm.mappable_gtt_total);
+		   dev_priv->mm.gtt_total,
+		   dev_priv->mm.gtt_mappable_end - dev_priv->mm.gtt_start);
 
 	mutex_unlock(&dev->struct_mutex);
 

drivers/gpu/drm/i915/i915_drv.h

···
 
 		/* accounting, useful for userland debugging */
 		size_t gtt_total;
-		size_t mappable_gtt_total;
 		size_t object_memory;
 		u32 object_count;
 	} mm;

drivers/gpu/drm/i915/i915_gem_gtt.c

···
 	dev_priv->mm.gtt_start = start;
 	dev_priv->mm.gtt_mappable_end = mappable_end;
 	dev_priv->mm.gtt_total = end - start;
-	dev_priv->mm.mappable_gtt_total = mappable_end - start;
 
 	/* Clear any non-preallocated blocks */
 	drm_mm_for_each_hole(entry, &dev_priv->mm.gtt_space,