I just did something very similar. If you have a working communication channel between PRU and user space anyway (probably RPMsg), you could read the location from the PRU code using:
myvar = resourceTable.shared_mem.pa;
and communicate that address to user space using RPMsg.
If you're anyway writing a Linux kernel driver, you could also extract the address from the remoteproc driver and expose it, for example, through sysfs, but I don't have a working solution for that.