net: sh-eth: Add support R7S72100 of rmobile

The R7S72100 of ARM SoC that Renesas manufactured has one Ether port.
This has the same IP SH-Ether. This patch adds support of the R7S72100
in SH-Ether.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>