dt-bindings: mailbox: qcom: add one more clock provider for IPQ mailbox

Mailbox controller present in the IPQ SoCs takes the GPLL0 clock also as
an input. Document the same.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Kathiravan Thirumoorthy <quic_kathirav@quicinc.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

Documentation/devicetree/bindings/mailbox/qcom,apcs-kpss-global.yaml

@@ -125,10 +125,12 @@ allOf:
           items:
             - description: primary pll parent of the clock driver
             - description: XO clock
+            - description: GCC GPLL0 clock source
         clock-names:
           items:
             - const: pll
             - const: xo
+            - const: gpll0
 
   - if:
       properties: