MIPS: Loongson64: DTS: Fix PCIe port nodes for ls7a

Add various required properties to silent warnings:

arch/mips/boot/dts/loongson/loongson64-2k1000.dtsi:116.16-297.5: Warning (interrupt_provider): /bus@10000000/pci@1a000000: '#interrupt-cells' found, but node is not an interrupt provider
arch/mips/boot/dts/loongson/loongson64_2core_2k1000.dtb: Warning (interrupt_map): Failed prerequisite 'interrupt_provider'

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>