net: ethernet: ti: cpsw: use devm_alloc_etherdev_mqs()

Use devm_alloc_etherdev_mqs() and simplify code.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>