drivers: net: cpsw: remove pm runtime calls from suspend callbacks

PM runtime is properly handled in cpsw_ndo_open/stop(), as result it
isn't required to duplicate these calls in .suspend()/.resume()
callbacks. Moreover, it might cause unnecessary RPM resume of CPSW
during System suspend in the case it's already suspended because
all ethX interfaces are down already, before System suspend started.

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