net: ethernet: ti: cpsw: move cpsw definitions in priv header

As a preparatory patch to add a switchdev based cpsw driver move the common
header definitions to cpsw_priv.h. The plan is to develop a new driver on
switchdev driver model and obsolete the current cpsw driver after all
required functions are added to the new driver. This patch allows the same
header file to be re-used on both drivers during the transition period.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>