sh_eth: get SH7724 support out of #ifdef

Get the SH7724 code/data in the driver out of #ifdef by adding "r8a7724-ether"
to the platform driver's ID table. Change the Ether platform device's name in
the SH platform code accordingly.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>