The serial port can be accessed on U2713, pin 2 is RX, pin 3 is TX, device node is /dev/ttyS1.
I use it with a 3.3V USB-to-UART adapter, but any voltage between 1.2 and 3.6 should be fine, thanks to the TI voltage-level translator TXB0104.
There is also a second uart connected to J151 (ttyS0), but that one has no voltage-level-translator and runs with 2V. (TX is on pin 9 of J151, no idea where RX is).
I'm still trying to redirect the boot console to ttyS1, i think i have to recompile uboot.
Patching u-boot worked, I have the boot console on ttyS1.