net: marvell: mvpp2: Fix wrong SerDes reconfiguration order

Commit bfe301eb ("net: mvpp2: convert to use
mac_prepare()/mac_finish()") introduced a bug wherein it leaves the MAC
RESET register asserted after mac_finish(), due to wrong order of
function calls.

Before it was:
  .mac_config()
    mvpp22_mode_reconfigure()
      assert reset
    mvpp2_xlg_config()
      deassert reset

Now it is:
  .mac_prepare()
  .mac_config()
    mvpp2_xlg_config()
      deassert reset
  .mac_finish()
    mvpp2_xlg_config()
      assert reset

Obviously this is wrong.

This bug is triggered when phylink tries to change the PHY interface
mode from a GMAC mode (sgmii, 1000base-x, 2500base-x) to XLG mode
(10gbase-r, xaui). The XLG mode does not work since reset is left
asserted. Only after
  ifconfig down && ifconfig up
is called will the XLG mode work.

Move the call to mvpp22_mode_reconfigure() to .mac_prepare()
implementation. Since some of the subsequent functions need to know
whether the interface is being changed, we unfortunately also need to
pass around the new interface mode before setting port->phy_interface.

Fixes: bfe301eb ("net: mvpp2: convert to use mac_prepare()/mac_finish()")
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>