net: mvpp2: dynamic reconfiguration of the comphy/GoP/MAC

This patch adds logic to reconfigure the comphy/GoP/MAC when the link
state is updated at runtime. This is very useful on boards where many
link speed are supported: depending on what is negotiated the PPv2
driver will automatically reconfigures the link between the PHY and the
MAC.

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