ARM: dts: DRA7: Add "linux,pci-domain" property for pci dt nodes

Since DRA7 has multiple PCIe Rootcomplex, add "linux,pci-domain"
property to assign a PCI domain number to each of the host
bridges.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>