In preparation for implementing lockless slab shrink,
we need to dynamically allocate the i915_gem_mm shrinker,
so that it can be freed asynchronously by using kfree_rcu().
Then it doesn't need to wait for RCU read-side critical
section when releasing the struct drm_i915_private.
Signed-off-by: Qi
From: Qi Zheng
In preparation for implementing lockless slab shrink,
we need to dynamically allocate the i915_gem_mm shrinker,
so that it can be freed asynchronously by using kfree_rcu().
Then it doesn't need to wait for RCU read-side critical
section when releasing the struct drm_i915_private.
