net: ethernet: ti: cpsw: move platform data struct to .c file

CPSW platform data struct cpsw_platform_data and struct cpsw_slave_data are
used only incide cpsw.c module, so move these definitions there.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>