My 4/110 hasn't successfully booted a kernel in a long time. I've
been meaning to send a PR, but never got around to it.

The first problem is that, with a serial console, things will hang
as soon as the kernel switched to a 'native' serial console (i.e.
after zs has been probed).

There was a rearrangement of zs code in around february as far as I can
remember, and after reverting that, serial console worked after the
probe of zs.

However, it then panicked at 'ie at vme0' probe, with a message
I can't remember. I gave up and haven't had time since to look at it.

I did notice a zs commit recently mentioning 4/100, I don't know
if it fixes my serial console problem.

- Frank