ASoC: dt-bindings: nau8822: add nuvoton,spk-btl property to dtschema

Add nuvoton,spk-btl to configure the two loudspeaker outputs
as Bridge Tied Load

Cc: David Lin <[e-mail]>
Signed-off-by: Emanuele Ghidoli <[e-mail]>
Signed-off-by: Francesco Dolcini <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

Documentation/devicetree/bindings/sound/nuvoton,nau8822.yaml

···
   reg:
     maxItems: 1
 
+  nuvoton,spk-btl:
+    description:
+      If set, configure the two loudspeaker outputs as a Bridge Tied Load output
+      to drive a high power external loudspeaker.
+    $ref: /schemas/types.yaml#/definitions/flag
+
 required:
   - compatible
   - reg