net: sh-eth: add support for SH7753

SH7753 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>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>