drivers: net: cpsw: dual_emac: in suspend/resume bring down/up all the netdev

During suspend and resume in Dual EMAC, second port is not working as in
suspend/resume only the first slave netdev is closed and opened. So bring
down and up all the interfaces that are up during suspend/resume.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Tested-by: Nishanth Menon <nm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>