PCI: mvebu: Convert to PCI emulated bridge config space

Convert the pci-mvebu driver to use the pci-bridge-emul logic, that
helps emulating a root port PCI bridge configuration space.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>