PCI: aardvark: Implement emulated root PCI bridge config space

The PCI controller in the Marvell Armada 3720 does not implement a
software-accessible root port PCI bridge configuration space. This
causes a number of problems when using PCIe switches or when the Max
Payload size needs to be aligned between the root complex and the
endpoint.

Implementing an emulated root PCI bridge, like is already done in the
pci-mvebu driver for older Marvell platforms allows to solve those
issues, and also to support features such as ASR, PME, VC, HP.

Signed-off-by: Zachary Zhang <zhangzg@marvell.com>
[Thomas: convert to the common emulated PCI bridge logic.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>