[POWERPC] Add flatdevtree source

Add the latest version of the flatdevtree code and corresponding glue.

A phandle table now tracks values returned by ft_find_device().
The value returned by ft_find_device() is a phandle which is really
an index into the phandle table.  The phandle table contains the address
of the corresponding node.  When the flat dt is edited/moved, the node
pointers in the phandle table are updated accordingly so no phandles kept
by the caller become stale.

Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>