[POWERPC] Fix bug adding properties with flatdevtree.c's ft_set_prop()

[POWERPC] Fix bug adding properties with flatdevtree.c's ft_set_prop()

ft_set_prop() from flatdevtree.c in the zImage wrapper will either
replace an existing property in the flat device tree, or add a new
property definiion if the given property isn't present.

However, when adding properties, it adds the property definition
immediately before the node's END_NODE tag, potentially after any
subnode definitions for the node.  This confuses the kernel flat tree
parser in prom.c which assumes that all property definitions for a
node come before all subnode definitions.

This patch corrects ft_set_prop() so that it adds new properties
before the first subnode, instead of before the END_NODE tag.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Scott Wood <scottwood@freescale.com>
Acked-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>