net: sh_eth: add support for SH7752

SH7752 has two fast ethernet controllers and two gigabit ethernet
controllers. It is similar to SH7757.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>