dt-bindings: gpio: msc313: Add compatible for ssd20xd

Add a compatible string for "ssd20xd" for the SigmaStar SSD201
and SSD202D chips. These chips are the same die with different
memory bonded so they don't need their own strings.
Signed-off-by: Daniel Palmer <daniel@0x0f.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

Documentation/devicetree/bindings/gpio/mstar,msc313-gpio.yaml

@@ -14,7 +14,9 @@ properties:
     pattern: "^gpio@[0-9a-f]+$"
 
   compatible:
-    const: mstar,msc313-gpio
+    enum:
+      - mstar,msc313-gpio
+      - sstar,ssd20xd-gpio
 
   reg:
     maxItems: 1