ipc_service: Add ipc_service_close_instance function

This function allows the application to close an ipc_service instance.
It is intended for use when the remote agent it is communicating with
has gone down and allows for cleanup.
It first checks that the endpoints have been separately deregistered
with the instance using the deregister_endpoint function before
calling into previously added functions in ipc_static_vrings.c
and ipc_rpmsg.c to close those instances.

Signed-off-by: Jackson Cooper-Driver <jackson.cooper---driver@amd.com>