sh_eth: get rid of 'sh_eth_cpu_data::shift_rd0'

After checking all  the available manuals,  I have enough information to
conclude  that the 'shift_rd0' flag is only relevant  for the Ether cores
supporting so called "intelligent checksum" (and hence having CSMR) which
is indicated  by the 'hw_crc' flag.  Since  all the relevant SoCs now have
both these flags set, we can  at last  get  rid of the former flag...

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