hikey-kernel: Reorganize prebuilt kernel directory am: 650d521ebf am: 11b1475093 am: aacd3751d4 am: f21464657d

Original change: https://android-review.googlesource.com/c/device/linaro/hikey-kernel/+/1324300

Change-Id: I846ff22d4a014e523d25d2cc1b9f5fea00f77d6f