arm64: dts: marvell: Add Aardvark PCIe support for Armada 3700

Add the SoC-level description of the PCIe controller found on the Marvell
Armada 3700 and enable this PCIe controller on the development board for
this SoC.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>