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

* commit 'd58957c6d543ffcd5f25e932909f11fab7dd69e6':
  hikey-kernel: Update prebuilt kernel to 4.1.15 (d71f3d2)

Change-Id: I3af2f026bacbc66669f61c01bc113e67ccaec30b