net: mvpp2: Enable PHY polling mode on PPv2.2

net: mvpp2: Enable PHY polling mode on PPv2.2

Testing shows, that PHY polling needs to be enabled on Armada 7k/8k.
Otherwise ethernet transfers will not work correctly. PHY polling
is enabled per default after reset, so we do not need to specifically
enable it, but this makes it clearer.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Stefan Chulski <stefanc@marvell.com>
Cc: Kostya Porotchkin <kostap@marvell.com>
Cc: Nadav Haklai <nadavh@marvell.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>