Merge "bindings: update documentation for support-legacy_smc"

Required properties:

- compatible : Should be "qcom,smcinvoke"

- qcom,support-legacy_smc : indicates that secure side uses QCOM_SCM_SMCINVOKE_INVOKE_LEGACY (value = 0x00) for smcinvoke

			    functionality.

Example:

	qcom_smcinvoke: smcinvoke@87900000 {

		compatible = "qcom,smcinvoke";

	};

Example: For targets where secure side runs with QCOM_SCM_SMCINVOKE_INVOKE_LEGACY cmd id

	qcom_smcinvoke: smcinvoke@87900000 {

                compatible = "qcom,smcinvoke";

		qcom,support-legacy_smc;

        };