drivers: net: cpsw: ndev: fix accessing to suspended device

The CPSW might be suspended by RPM if all ethX interfaces are down,
but it still could be accesible through net_device_ops interfce. In
this case net_device_ops operations requiring registers access will
cause L3 errors and CPSW crash.

Hence, fix it by adding RPM get/put calls in net_device_ops callbacks
which need to access CPSW registers: .ndo_set_mac_address(),
.ndo_vlan_rx_add_vid(), .ndo_vlan_rx_kill_vid().

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