PCI: mvebu: add support for Marvell Dove SoCs

This patch adds a compatible for the PCIe controller found on Marvell
Dove SoCs. Binding documentation and Kconfig entry are also updated.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>