ARM: meson: document meson8 compatible properties

Add device tree bindings documentation for Amlogic Meson8 SoCs.
Signed-off-by: Beniamino Galvani <b.galvani@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Carlo Caione <carlo@caione.org>

Documentation/devicetree/bindings/arm/amlogic.txt

@@ -2,7 +2,9 @@ Amlogic MesonX device tree bindings
 -------------------------------------------
 
 Boards with the Amlogic Meson6 SoC shall have the following properties:
+  Required root node property:
+    compatible: "amlogic,meson6"
 
-Required root node property:
-
-compatible = "amlogic,meson6";
+Boards with the Amlogic Meson8 SoC shall have the following properties:
+  Required root node property:
+    compatible: "amlogic,meson8";