arm: mvebu: db-mv784mp-gp: Enable PCI support

This patch enabled the MVEBU PCIe support on the db-mv784mp-gp AXP
eval board. It also enabled the Intel E1000 driver support and
adds the initialization of PCIe network controllers to the
board code.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Anton Schubert <anton.schubert@gmx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>