[POWERPC] bootwrapper: Rename ft_node_add() to ft_get_phandle().

This name better reflects what the function does, which is to
look up the phandle for an internal node pointer, and add it to the
internal pointer to phandle table if not found.

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