[PATCH][OF] Add of_device_is_available function

[David Miller]

From: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Date: Wed, 27 Feb 2008 08:45:37 +1100

> I doubt we do that. Properties that contain things like ranges, or "reg"
> properties are expected to be of a size that is a multiple of
> #size-cells/#address-cells and I'm not sure that won't break things here
> or there if they suddenly get one more byte..
> 
> Or do you mean you/we are appending that-without- changing the length
> field ?

Right, simply don't change the length field.  Put the zero byte
at offset "length + 1"

It's stupid to validate NULL termination everywhere when we
can make it an invariant in one spot.