dtc: Generate useful error message for properties after subnodes

[Jon Loeliger]

So, like, the other day David Gibson mumbled:
> On several occasions, I've accidentally put properties after subnodes
> in a dts file.  I've then spent ages thinking that the resulting
> syntax error was because of something else.
> 
> This patch arranges for this specific syntax error to generate a more
> specific and useful error message.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.

jdl