net: mvpp2: always disable both MACs when disabling a port

This patch modifies the port_disable() helper to always disable both the
GMAC and the XLG MAC when called. At boot time we do not know of a port
was enabled in the firmware/bootloader, and if so what mode was used
(hence which of the two MACs was used).

This also help in implementing a logic where all blocks are disabled
when not used, and only enabled regarding the current mode used on a
given port.

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