net: sh_eth: CPU dependency code collect to "struct sh_eth_cpu_data"

This improves readability by collecting CPU dependency code.

Signed-off-by: Yoshihiro Shimoda <shimoda.yoshihiro@renesas.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu.nobuhiro@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>