sh_eth: remove SH_ETH_HAS_TSU

Remove SH_ETH_HAS_TSU #define's and #ifdef's. Set three 'struct net_device_ops'
methods that depend on the presence of TSU basing on the 'tsu' field of 'struct
sh_eth_cpu_data'.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
[Sergei: made two method assignments one-liners, added the changelog, reworded
the subject, changing the prefix.]
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>