sh_eth: remove #ifdef around EDSR and GECMR bit definitions

Remove #ifdef around 'enum EDSR_BIT' and 'enum GECMR_BIT', replacing it with the
comments on which SoCs these registers exist.

SH7757 also has EDSR, so add a comment about it to 'enum EDSR_BIT'.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
[Sergei: folded in the former patch #2, updated the changelog, reworded the
subject, changing the prefix.]
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>