[U-Boot] Switch MVPP2 to use new MVMDIO

[nhed+uboot at starry.com]

This patchset includes several commits form Marvell's downstream repo
including Ken Ma's patch to replace the SMI implementation with his
own Marvell MDIO impolementation.  That MVMDIO implementation never
made it to upstream and has since been re-implemented by Alex
Marginean and seems to be in line for inclusion [1].  My last patch in
this set modified Ken's mvpp2 patch to use this new MVMDIO
implementation.  Few other mvpp2 patches picked as they seemed
important yet missing from upstream.

  [1] https://patchwork.ozlabs.org/cover/1136769/