mediatek: enable rootwait for cmcc rax3000m emmc version

Sometimes the mmc deivce may come up later than kernel attempts to
mount rootfs, resulting kernel panic. Enable rootwait to fix it.

Reported-by: Yangyu Chen <cyy@cyyself.name>
Signed-off-by: Tianling Shen <cnsztl@immortalwrt.org>
Link: https://github.com/openwrt/openwrt/pull/15077
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/mediatek/dts/mt7981b-cmcc-rax3000m-emmc.dtso

@@ -7,6 +7,13 @@
 	compatible = "cmcc,rax3000m", "mediatek,mt7981";
 
 	fragment@0 {
+		target = <&chosen>;
+		__overlay_ {
+			bootargs-append = " rootwait";
+		};
+	};
+
+	fragment@1 {
 		target = <&mmc0>;
 		__overlay__ {
 			bus-width = <8>;
@@ -22,7 +29,7 @@
 		};
 	};
 
-	fragment@1 {
+	fragment@2 {
 		target = <&pio>;
 		__overlay__ {
 			mmc0_pins_default: mmc0-pins {

target/linux/mediatek/dts/mt7981b-cmcc-rax3000m.dts

@@ -21,7 +21,7 @@
 		serial0 = &uart0;
 	};
 
-	chosen {
+	chosen: chosen {
 		stdout-path = "serial0:115200n8";
 	};