sh_eth: use Gigabit register map for R7S72100

The register maps for the Gigabit controllers and the Ether one used on
RZ/A1  (AKA R7S72100) are identical except for GECMR which is only present
on the true GEther controllers.  We no longer use the register map arrays
to determine if a given register exists,  and have added the GECMR flag to
the 'struct sh_eth_cpu_data' in the previous patch, so we're ready to drop
the R7S72100 specific register map -- this saves 216 bytes of object code
(ARM gcc 4.8.5).

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Tested-by: Chris Brandt <chris.brandt@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>