Sort nodes.

If node address is present
   * Sort by node address, grouping all nodes with the same compat string
     and sorting the group alphabetically.
Else
   * Sort alphabetically

This should not have any run-time effect.
Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
[geert: Sort i2c slave nodes]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>