net: renesas: rswitch: Add phy_power_{on,off}() calling

Some Ethernet PHYs (like marvell10g) will decide the host interface
mode by the media-side speed. So, the rswitch driver needs to
initialize one of the Ethernet SERDES (r8a779f0-eth-serdes) ports
after linked the Ethernet PHY up. The r8a779f0-eth-serdes driver has
.init() for initializing all ports and .power_on() for initializing
each port. So, add phy_power_{on,off} calling for it.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>