net: mvpp2: reset the MACs when reconfiguring a port

This patch makes sure both PPv2 MACs (GMAC + XLG MAC) are set in reset
while a port is reconfigured. This is done so that we make sure a MAC is
in a reset state when not used, as only one of the two will be set out
of reset after the port is configured properly.

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>