hikey-kernel: Update prebuilt kernel to 4.1.15 (d71f3d2) am: d29bfaf422
am: 136f610aa0

* commit '136f610aa0e3997f6242adee02f6ec6b23639755':
  hikey-kernel: Update prebuilt kernel to 4.1.15 (d71f3d2)

Change-Id: I474bcd7cd42194b9fb171ed8be45ea66d5f02c68