How can I enable UART 1 and 2?

[theaet...@gmail.com]

I'm booting off an SD card (debian 8.7, jessie) and I've disabled HDMI by uncommenting dtb=am335x-boneblack-emmc-overlay.dtb in the /boot/uEnv.txt.

The system now boots with most every gpio exported, which is fine in most cases, except I need UART 1 and 2. I can see that these gpios are exported, but I can't unexport them, and attempting to load the device tree overlays for UART 1 and 2 also fails.

How can I get access to these UARTs?