There are two kinds of locking sequence.

One is in the thread which is started by vfio ioctl to do
the iommu unmapping. The locking sequence is:
	down_read(&group_lock) ----> mutex_lock(&cached_lock)

The other is in the vfio release thread which will unpin all
the cached pages. The lock sequence is:
	mutex_lock(&cached_lock) ---> down_read(&group_lock)

And, the cache_lock is used to protect the rb tree of the cache
node and doing vfio unpin doesn't require this lock. Move the
vfio unpin out of the cache_lock protected region.

v2:
- use for style instead of do{}while(1). (Zhenyu)

Fixes: f30437c5 ("drm/i915/gvt: add KVMGT support")
Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: stable@vger.kernel.org # v4.10+
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>