net: ethernet: ti: cpsw: move platform data and slaves info to cpsw_common

These data are common for net devs in dual_emac mode. No need to hold
it for every priv instance, so move them under cpsw_common.

Signed-off-by: Ivan Khoronzhuk <[email protected]>
Reviewed-by: Mugunthan V N <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: ikhorn