net: mvpp2: add FCA periodic timer configurations

Flow Control periodic timer would be used if port in
XOFF to transmit periodic XOFF frames.

Signed-off-by: Stefan Chulski <stefanc@marvell.com>
Acked-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: David S. Miller <davem@davemloft.net>