dtc: Implement path references

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@gibson.dropbear.id.au>
8 files changed