dt-bindings: net: realtek-bluetooth: Add RTL8821CS

Add compatible string for RTL8821CS for existing Realtek Bluetooth
driver.

Signed-off-by: Chris Morgan <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Alistair Francis <[e-mail]>
Signed-off-by: Luiz Augusto von Dentz <[e-mail]>

Documentation/devicetree/bindings/net/realtek-bluetooth.yaml

···
 $id: http://devicetree.org/schemas/net/realtek-bluetooth.yaml#
 $schema: http://devicetree.org/meta-schemas/core.yaml#
 
-title: RTL8723BS/RTL8723CS/RTL8822CS Bluetooth
+title: RTL8723BS/RTL8723CS/RTL8821CS/RTL8822CS Bluetooth
 
 maintainers:
   - Vasily Khoruzhick <[e-mail]>
   - Alistair Francis <[e-mail]>
 
 description:
-  RTL8723CS/RTL8723CS/RTL8822CS is WiFi + BT chip. WiFi part is connected over
-  SDIO, while BT is connected over serial. It speaks H5 protocol with few
-  extra commands to upload firmware and change module speed.
+  RTL8723CS/RTL8723CS/RTL8821CS/RTL8822CS is a WiFi + BT chip. WiFi part
+  is connected over SDIO, while BT is connected over serial. It speaks
+  H5 protocol with few extra commands to upload firmware and change
+  module speed.
 
 properties:
   compatible:
-    enum:
-      - realtek,rtl8723bs-bt
-      - realtek,rtl8723cs-bt
-      - realtek,rtl8723ds-bt
-      - realtek,rtl8822cs-bt
+    oneOf:
+      - enum:
+          - realtek,rtl8723bs-bt
+          - realtek,rtl8723cs-bt
+          - realtek,rtl8723ds-bt
+          - realtek,rtl8822cs-bt
+      - items:
+          - enum:
+              - realtek,rtl8821cs-bt
+          - const: realtek,rtl8822cs-bt
 
   device-wake-gpios:
     maxItems: 1