ARM: dts: uniphier: add pinctrl groups of ethernet phy mode

Add pinctrl groups of ethenet phy mode, such as "ether_rgmii", "ether_rmii",
and "ether_mii".

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>