hikey-kernel: Update prebuilt kernel to 4.1.15 (d71f3d2) am: d58957c6d5
am: 66401fcd7b

* commit '66401fcd7b5dfeff76fd050befd365538d7062e1':
  hikey-kernel: Update prebuilt kernel to 4.1.15 (d71f3d2)

Change-Id: I75b845b61703ccdc93900858a96f1ebcfd0badd9