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";
       };