dtc: Implement path references

[Jon Loeliger]

So, like, the other day David Gibson mumbled:
> This patch extends dtc syntax to allow references (&label, or
> &{/full/path}) directly within property definitions, rather than
> inside a cell list.  Such references are expanded to the full path of
> the referenced node, as a string, instead of to a phandle as
> references within cell lists are evaluated.
> 
> A testcase is also included.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Excellent.  Very timely! :-)

Applied.

jdl