dt-bindings: arm: syna: add support for the AS370 SoC

The AS370 SoC is a new derivative of the berlin family. However, the
SoC isn't named as berlin*.
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Reviewed-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/arm/syna.txt

-Marvell Berlin SoC Family Device Tree Bindings
+Synaptics SoC Device Tree Bindings
+
+According to https://www.synaptics.com/company/news/conexant-marvell
+Synaptics has acquired the Multimedia Solutions Business of Marvell, so
+berlin SoCs are now Synaptics' SoCs now.
+
 ---------------------------------------------------------------
 
 Work in progress statement:
@@ -13,6 +18,10 @@ stable binding/ABI.
 
 ---------------------------------------------------------------
 
+Boards with the Synaptics AS370 SoC shall have the following properties:
+  Required root node property:
+    compatible: "syna,as370"
+
 Boards with a SoC of the Marvell Berlin family, e.g. Armada 1500
 shall have the following properties: