sh_eth: remove 'register_type' field from 'struct sh_eth_plat_data'

Now that the 'register_type' field of the 'sh_eth' driver's platform data is not
used by the driver anymore, it's time to remove it and  its initializers from
the SH platform code. Also  move *enum* declaring values for this  field from
<linux/sh_eth.h>  to  the  local driver's  header file as they're only needed
by the driver itself  now...

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