dt-bindings: add compatible string for Allwinner V3s SoC

The compatible string for Allwinner V3s SoC used to be missing.

Add it to the binding document.

Fixes: b074fede ("arm: sunxi: add support for V3s SoC")
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

Documentation/devicetree/bindings/arm/sunxi.txt

@@ -14,6 +14,7 @@ using one of the following compatible strings:
   allwinner,sun8i-a83t
   allwinner,sun8i-h2-plus
   allwinner,sun8i-h3
+  allwinner,sun8i-v3s
   allwinner,sun9i-a80
   allwinner,sun50i-a64
   nextthing,gr8