I was successful until point 3 of the UEFI guide
Install ser2net. Use telnet as the console since UEFI will output window that fails to display in minicom.
$sudo apt-get install ser2net
$sudo vi /etc/ser2net.conf
Append one line for serial-over-USB in below.
2004:telnet:0:/dev/ttyUSB0:115200 8DATABITS NONE 1STOPBIT banner
Open the console.
$telnet localhost 2004
And you could open the console remotely, too.
So, now what should I do? I connect the board to the PC with the USB...
build_hikey_960$ telnet localhost 2004
Connected to localhost.
Escape character is '^]'.
Connection closed by foreign host.