dt-bindings: pci: add PHY properties to Armada 7K/8K controller bindings

Armada CP110 PCIe controller can have from one to four PHYs for
configuring SERDES lanes (PCIe x1, PCIe x2 or PCIe x4). Describe the
phys and phy-names properties in the bindings.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>