net: mvpp2: Add GoP and NetC support for ports 2 & 3 (RGMII & SGMII)

This patch adds the GoP (Group of Ports) and NetC (Net Complex) setup to
the Marvell mvpp2 ethernet driver. This code is mostly copied from the
Marvell U-Boot version and was written by Stefan Chulski. Please
note that only RGMII and SGMII support have been added, as these are
the only interfaces that this code has been tested with.
Signed-off-by: NStefan Roese <sr@denx.de>
Cc: Stefan Chulski <stefanc@marvell.com>
Cc: Kostya Porotchkin <kostap@marvell.com>
Cc: Nadav Haklai <nadavh@marvell.com>
Acked-by: NJoe Hershberger <joe.hershberger@ni.com>