brcm63xx: move the bootargs into the dtb files

Instead of using a fixed commandline, allow one per device.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>

target/linux/brcm63xx/dts/hg556a-a.dts

@@ -8,6 +8,10 @@
 	model = "Huawei EchoLife HG556a (version A)";
 	compatible = "huawei,hg556a-a", "brcm,bcm6358";
 
+	chosen {
+		bootargs = "root=/dev/mtdblock2 rootfstype=squashfs,jffs2 noinitrd console=ttyS0,115200";
+	};
+
 	gpio-keys-polled {
 		compatible = "gpio-keys-polled";
 		#address-cells = <1>;