dt-bindings: arm: qcom: Document SDX55 platform and boards

Document the SDX55 platform binding and also the boards using it.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20201126083138.47047-2-manivannan.sadhasivam@linaro.orgSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Documentation/devicetree/bindings/arm/qcom.yaml

@@ -40,6 +40,7 @@ description: |
         sdm630
         sdm660
         sdm845
+        sdx55
         sm8250
 
   The 'board' element must be one of the following strings:
@@ -167,6 +168,11 @@ properties:
               - xiaomi,lavender
           - const: qcom,sdm660
 
+      - items:
+          - enum:
+              - qcom,sdx55-mtp
+          - const: qcom,sdx55
+
       - items:
           - enum:
               - qcom,ipq6018-cp01-c1