mii: Convert printks to netdev_info

Add a bit more data to the output.
Convert string speeds to integer.
Object size reduced a tiny bit.
$ size drivers/net/mii.o*
   text	   data	    bss	    dec	    hex	filename
   4155	     56	   1000	   5211	   145b	drivers/net/mii.o.new
   4184	     56	   1000	   5240	   1478	drivers/net/mii.o.old

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>