settings objects: support multiple interfaces

A settings object had the limitation that it could implement a single,
corresponding settings interface. This was found to be too restrictive
because there are use-cases (such as in the boot settings area) that
would simplify describing settings with objects that can implement more
than one interface.

This commit adds the ability for settings objects to implement multiple
interfaces. The settings config yaml now should contain a list of
interface(s) under each settings object.

Change-Id: I90dec9e766e1afd1b0c8616e491832714bbd069d
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
2 files changed