arm: rmobile: alt: Add ethernet function B support

Ethernet function of Alt board can select normal and B by DIP switch
on board. But user need to set not only DIP switch but also pin function.
This adds pin function of Ethernet function B. This can select from Kconfig.

Signed-off-by: Mitsuhiro Kimura <mitsuhiro.kimura.kc@renesas.com>
Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>