Make sure we populate the initroot filesystem late enough

[Benjamin Herrenschmidt]

> USB controller issues? We used to have these really hard-to-debug problems 
> with the USB controller being active and having had the BIOS set up the 
> command queues etc. Really subtle. It's why we now have PCI quirks for 
> shutting up (most) USB controllers very early.

On powermacs or powerbooks, the USB controller is shut down by the
firmware when we call the "quiesce" OF call from prom_init.c, which
happens before the kernel relocates itself to 0 and takes over memory.
Unless we fucked up something in there, I wouldn't expect that to be the
cause.
 
> If there is some USB controller that we miss, or that sets up its command 
> chain to some unexpected area (so that USB is active and corrupting memory 
> even very early on), that could explain it.

Did we setup the OHCI controller when the crash happen ? Maybe we broke
something subtle in the USB stack ?

Ben.