[][MAC80211][infra][Add slot0 node under pcie0 node]

[Description]
Add slot0 node under pcie0 node

MT76 driver uses of_get_child_by_name API to enable SingSKU/Flash Mode.
PCIe WiFi device on MT7986 fails to get because there is no slot0 node.

[Release-log]
N/A

Change-Id: I3d25a522a016c155b2439f43930f5d1420e0fd2c
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/6056897
diff --git a/target/linux/mediatek/files-5.4/arch/arm64/boot/dts/mediatek/mt7986a.dtsi b/target/linux/mediatek/files-5.4/arch/arm64/boot/dts/mediatek/mt7986a.dtsi
index 9f86879..d50d25b 100644
--- a/target/linux/mediatek/files-5.4/arch/arm64/boot/dts/mediatek/mt7986a.dtsi
+++ b/target/linux/mediatek/files-5.4/arch/arm64/boot/dts/mediatek/mt7986a.dtsi
@@ -354,6 +354,10 @@
 			#address-cells = <0>;
 			#interrupt-cells = <1>;
 		};
+
+		slot0: pcie@0,0 {
+			reg = <0x0000 0 0 0 0>;
+		};
 	};
 
 	crypto: crypto@10320000 {