Mainline Kernel booting - Cannot access dev-ttyS0.device

Hi, I try to boot a mainline kernel on the TX1 like described in http://elinux.org/Jetson/TX1_Upstream_Kernel. I choosed the stable tree and checkout 4.9. After this I build the kernel, create one partition on my sdcard, drop an ubuntu rootfs (not the nvidia one, an “original” rootfs for arm64 from ubuntu) on it, copied the device tree to the board and created the extlinux.conf like described in the tutorial (all on an external sd card).

I can start, the kernel boots up. Also I’ve got the message ‘Welcome to Ubuntu 16.04.2 LTS’ on my uart output (for this, I used the tutorial of http://elinux.org/Jetson/TX1_Serial_Console.
But after a few moments and waiting for the response I got the message:
‘[Time] Timed out waiting for device dev-ttyS0.device.’ Also an dependency errro occurs, linking to the dev-ttyS0 device.
I think on this console the stdout, so I cannot login or do anything.
Does anybody knows about a similar issue or knows how to solve it?

P.S. I build the kernel with ‘CONFIG_FHANDLE=y’