Beaglebone Black - Maximum current supplied by 1.8V analog rail (Pin P9_32)?
To find the current capability of that pin, you need to look in the Sitara datasheet. The pin is called VDDA_ADC, and is specified for 10 milliamps.

However, I would not recommend putting a voltage divider on that signal without a buffer. Although that pin is often referred to as a "rail", it is actually the reference voltage to the ADC, so using it directly will add a path for noise into all eight ADC channels.

I would recommend adding an additional op-amp to buffer it prior to using it.