drivers: net: cpsw: drop host_port field from struct cpsw_priv

The host_port field is constantly assigned to 0 and this value has
never changed (since time when cpsw driver was introduced. More over,
if this field will be assigned to non 0 value it will break current
driver functionality.

Hence, there are no reasons to continue maintaining this host_port
field and it can be removed, and the HOST_PORT_NUM and ALE_PORT_HOST
defines can be used instead.

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