net: phy: realtek: Support RTL8366RB variant

The RTL8366RB is an ASIC with five internal PHYs for
LAN0..LAN3 and WAN. The PHYs are spawn off the main
device so they can be handled in a distributed manner
by the Realtek PHY driver. All that is really needed
is the power save feature enablement and letting the
PHY driver core pick up the IRQ from the switch chip.

Cc: Antti Seppälä <a.seppala@gmail.com>
Cc: Roman Yeryomin <roman@advem.lv>
Cc: Colin Leitner <colin.leitner@googlemail.com>
Cc: Gabor Juhos <juhosg@openwrt.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>