Add RPC demux component

To support multiple co-located service providers, the rpc_demux
may be used.  It presents a single input rpc_interface and
demultiplexes incoming call requests to 1..* attached outputs
using the interface_id parameter carried by the underlying
RPC.

Signed-off-by: Julian Hall <julian.hall@arm.com>
Change-Id: I03d7423892cd07d8a8fcd445dbb7dc7e62497455
6 files changed