sh: Fix compile error of Solution Engine

When I compiled Solution Engine, this become compile error
because plaform device of sh_eth device becomes enable.
When sh7710/sh7712 which could use sh_eth was chosen,
revised it so that platform device of sh_eth device became enable.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu.nobuhiro@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>