Saving 10 seconds on boot

[Graeme Gregory]

Thanks to some hints I got on #oe I think I have a method of saving us
10s of boot time.

The method is quite simple, we pre-fill the /dev directory with the
static devices built into the kernel that we know are there.

We then dont run udevtrigger/udevsettle in the init script.

The downside to this method is SD driver needs to be modular otherwise
we lose hotplug detection of the card/partitions. This of course means
root on SD cant be supported in this setup.

Graeme