Comment 1 for bug 1472798

All of these commits are in v3.18-rc4, and thus in 15.10's kernel.
I think the issue here is that you did not modprobe the module in the firstplace.
From a clean install do:
modprobe ibmpowernv

The reason this doesn't get autoloaded seems to be another issue here:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1452473

I looked into this a while back and it seems like there is a mismatch between the modalias and what OF provides.

Marking this a dup of that bug. Thanks