net: sh_eth: remove almost #ifdef of SH7763

The SH7763 has GETHER. So the specification of some registers differs than
other CPUs. This patch removes almost #ifdef of CONFIG_CPU_SUBTYPE_SH7763.
Then we are able to add other CPU's GETHER easily.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>