arm64: dts: meson-gxbb-nanopi-k2: add missing model

This fixes the following DT schemas check errors:
meson-gxbb-nanopi-k2.dt.yaml: /: 'model' is a required property
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

arch/arm64/boot/dts/amlogic/meson-gxbb-nanopi-k2.dts

@@ -10,6 +10,7 @@
 
 / {
 	compatible = "friendlyarm,nanopi-k2", "amlogic,meson-gxbb";
+	model = "FriendlyARM NanoPi K2";
 
 	aliases {
 		serial0 = &uart_AO;