ARM: dts: msm: Adding support to send messages to AOP using QMP transport

AOP set ddr interface:

-----------------

AOP set ddr is an interface to send data to the Always on

processor using QMP.

Required properties :

- compatible : must be "qcom,aop-set-ddr-freq"

- mboxes : list of QMP mailbox phandle and channel identifier tuples

- mbox-names : names of the listed mboxes

Example :

       aop-set-ddr-freq {

               compatible = "qcom,aop-set-ddr-freq";

               mboxes = <&qmp_aop 0>;

               mbox-names = "aop";

       };