I didn't realize you're using the precompiled u-boot from TI, sorry.
If the precompiled u-boot is built from the Arago u-boot repo, I don't
believe ttyO1 is enabled still (at least not in the Arago u-boot
master branch). There has been some action on the TI u-boot repo lately,
but none that I see fully enabling ttyO1. ttyO3 is enabled in Arago's
u-boot (it's used on the am335x_evm board) but not sure well that fits
your needs since it's not pinned out on the Bone headers.
You could probably write a script in your uEnv.txt to hit the registers
directly and enable ttyO1, but I think patching and compiling u-boot
might be faster and easier.
-Andrew