Should set storage policy to attributeAccessInterface for attributes of struct type for Matter

[bzbarsky-apple]

Currently attribute loading has this piece in prepareCluster in zcl-loader-silabs.js:

      let storagePolicy = dbEnum.storagePolicy.any
      if (context.listsUseAttributeAccessInterface && attribute.$.entryType) {
        storagePolicy = dbEnum.storagePolicy.attributeAccessInterface

We should do the same thing for cases when the type of attribute is a struct type, if the appropriate boolean is set in context (to restrict it to Matter).

The problem is that at this stage we don't know which types are structs yet, right?

@tecimovic