dtc: Plugin and fixup support

This patch enable the generation of symbols & local fixup information
for trees compiled with the -@ (--symbols) option.

Using this patch labels in the tree and their users emit information
in __symbols__ and __local_fixups__ nodes.

The __fixups__ node make possible the dynamic resolution of phandle
references which are present in the plugin tree but lie in the
tree that are applying the overlay against.

panto: The original alternative syntax patch required the use of an empty node
which is no longer required.
Numbering of fragments in sequence was also implemented.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Jan Luebbe <jlu@pengutronix.de>

Downloaded from https://www.marc.info/?l=devicetree&m=144061468601974&w=4
Change-Id: Ie10fee384914eb37711089a6b6eaca59faa4dbdc