net: dsa: b53: Define EEE register page

In preparation for migrating the EEE code from bcm_sf2 to b53, define the full
EEE register page and offsets within that page.

Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>