I'm in the same boat and unfortunately haven't found the time
to sail my way out of it just yet. What I do know is if I boot
with an old 3.18 kernel I have, everything works out okay again.
I believe it was mentioned already that this could be related to
the issue with binutils being used to build the newer kernel you
are trying to boot from that came with Stretch.
I downloaded Peter's 4.5.0-rc2
kernel, installed it, and updated my yaboot.conf but still the
same issue. But honestly I could have missed something when
configuring my system to boot from his newer kernel. Planning to
look at that again here this evening and peruse some logs to see
what pops out at me.
If nothing else I will re-install
Jessie, download and install Peter's 4.5.0-rc2 kernel, and then
complete the upgrade to stretch and continue booting from that
same kernel. Will post my results when I can.
Thanks Brock