Add "reg" properties to place-holder nodes with unit address defined for
R-Car M3-N SoC.

This silences the following DTC compiler warning:
Warning (unit_address_vs_reg): Node /soc/... has a unit name,
but no reg property
Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>