kernel-drm: resolve linked list operation contend issue

kernel-drm: resolve linked list operation contend issue

BZ: 38174

Linked list operation need be protected with spin_lock,
otherwise it will cause random contend issue.

Change-Id: I61102fe9f9e5c984d48046530aa893eb5992a42c
Signed-off-by: Fei Jiang <fei.jiang@intel.com>
Reviewed-on: http://android.intel.com:8080/51050
Reviewed-by: Zeng, Li <li.zeng@intel.com>
Reviewed-by: Ding, Haitao <haitao.ding@intel.com>
Tested-by: Ding, Haitao <haitao.ding@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>