Add RPC caller and RPC caller session components

Change rpc_caller_interface to follow the new RPC protocol's primitives.
Introduce rpc_caller_session as a session layer built on top of the
rpc_caller_interface. An opened session is tied to an interface of an
RPC endpoint.

Signed-off-by: Imre Kis <imre.kis@arm.com>
Change-Id: Ibd75998d6a9d511b4adc79274cce34b59d9730f8
7 files changed