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 <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Reviewed-by: Linus Walleij <[e-mail]>
Signed-off-by: Bartosz Golaszewski <[e-mail]>

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

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