dtc: Accept NOPs in dtb input regardless of version

[Jon Loeliger]

So, like, the other day David Gibson mumbled:
> Since Milton's patch, dtc will accept (and, correctly, ignore) NOP
> tags when given dtb input v16 or later.  However, although NOPs
> weren't defined in earlier versions, they're not ambiguous, so should
> be accepted there as well.  This patch does so, printing a mere
> warning when finding NOPs in a too-early dtb version.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.

Thanks,
jdl