Replace se-proxy service backends with stubs

To facilitate the development of proxy backends that will
communicate with a remote secure element, the se-proxy
deployment has been modified to use stub components that
honour all service provider dependencies but don't do
anything.  This simplifies the se-proxy built image in
preparation for adding the se service clients.

Signed-off-by: Julian Hall <julian.hall@arm.com>
Change-Id: I2dac1e295814839d4c7dccf4120667186d7ea6de
34 files changed