MIPS: Loongson64: Add ISA node for LS7A PCH

Although currently we're not enabling any ISA device in devicetree,
but this node is required to express the ranges of address reserved
for ISA.

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

arch/mips/boot/dts/loongson/ls7a-pch.dtsi

@@ -367,5 +367,12 @@
 				interrupt-map = <0 0 0 0 &pic 39 IRQ_TYPE_LEVEL_HIGH>;
 			};
 		};
+
+		isa {
+			compatible = "isa";
+			#address-cells = <2>;
+			#size-cells = <1>;
+			ranges = <1 0 0 0x18000000 0x20000>;
+		};
 	};
 };