Add generic RPC layer

Adds generic RPC caller and endpoint. This is the base for specialized
RPC communication using e.g. FF-A messaging. The protocol description
is implemented in two flavours: packed C structures and protobuf.

Change-Id: I17f450b7272bd4008fc20fe8f716a253f6754000
Signed-off-by: Julian Hall <julian.hall@arm.com>
12 files changed