bindings: spmi: spmi-pmic-arb: Add description for "qcom,mid"

Add a description for the "qcom,mid" property which corresponds
to the SPMI master ID of the SPMI PMIC arbiter controller. It is
most useful in systems with multiple masters, e.g. when there are
multiple SoCs connected to a single SPMI bus.

Change-Id: I376e6f569f9bbea44ba3930480a330fb1dd2c2de
Signed-off-by: Ayyagari Ushasreevalli <quic_aushasre@quicinc.com>

bindings/spmi/qcom,spmi-pmic-arb.yaml

@@ -85,6 +85,13 @@ properties:
     description: >
       which of the PMIC Arb provided channels to use for accesses
 
+  qcom,mid:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    minimum: 0
+    maximum: 3
+    description: >
+      SPMI master ID of this controller.
+
 required:
   - compatible
   - reg-names