sh_eth: enable wake-on-lan for r8a7740/armadillo

Geert Uytterhoeven reported WoL worked on his Armadillo board.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: David S. Miller <davem@davemloft.net>