bcm63xx: move dts-v1 statement to top-level DTSI files

The "/dts-v1/;" identifier is supposed to be present once at the
top of a device tree file after the includes have been processed.

Like done for other targets recently, put the dts-v1 statement
into the top-level SoC-based DTSI files, and remove all other
occurences.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/bcm63xx/dts/bcm6362.dtsi

@@ -1,3 +1,5 @@
+/dts-v1/;
+
 / {
 	#address-cells = <1>;
 	#size-cells = <1>;