drm/i915: Make i915_vma_destroy() static

i915_vma_destroy() is now not used outside of i915_vma.c so we can
remove the export and make the function static.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170616123508.12673-1-chris@chris-wilson.co.ukReviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>

drivers/gpu/drm/i915/i915_vma.c

@@ -576,7 +576,7 @@ int __i915_vma_do_pin(struct i915_vma *vma,
 	return ret;
 }
 
-void i915_vma_destroy(struct i915_vma *vma)
+static void i915_vma_destroy(struct i915_vma *vma)
 {
 	GEM_BUG_ON(vma->node.allocated);
 	GEM_BUG_ON(i915_vma_is_active(vma));

drivers/gpu/drm/i915/i915_vma.h

@@ -236,7 +236,6 @@ bool i915_vma_misplaced(const struct i915_vma *vma,
 void __i915_vma_set_map_and_fenceable(struct i915_vma *vma);
 int __must_check i915_vma_unbind(struct i915_vma *vma);
 void i915_vma_close(struct i915_vma *vma);
-void i915_vma_destroy(struct i915_vma *vma);
 
 int __i915_vma_do_pin(struct i915_vma *vma,
 		      u64 size, u64 alignment, u64 flags);