I had my HiKey board booting from sdcard. I had HiKey Xen + Centos and these are the instructions: https://github.com/Jeeppler/xen-note/blob/master/arm64/hikey/hikey-xen-centos.md
Everything was fine. Then I flashed aosp on the HiKey with fastboot using these instructions: https://source.android.com/setup/devices#620hikey
Now in the boot time my board doesn’t see the sd card any more and boots directly to the android. Previously, I had these boot options in the boot time:
 boot from eMMC
 boot from SD card
 Boot Manager
But now it jumps directly to Android without showing boot options.