pci: pci_mvebu: Add DM_PCI support and move CONFIG_PCI_MVEBU to defconfig

This patch adds DM_PCI support to the MVEBU PCIe driver. This is
necessary, since all PCI drivers have to be moved to DM (driver model)
until the v2019.07 release.

To not break git bisect'ablility, this patch also moves CONFIG_PCI_MVEBU
from config headers to the defconfig files.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Dirk Eibach <dirk.eibach@gdsys.cc>
Cc: Mario Six <mario.six@gdsys.cc>
Cc: Chris Packham <chris.packham@alliedtelesis.co.nz>
Cc: Phil Sutter <phil@nwl.cc>
Cc: Marek Behún <marek.behun@nic.cz>
Cc: VlaoMao <vlaomao@gmail.com>