Missing testcases for VALID commands issued on UNSUPPORTED platforms
Currently there are testcases that issue INVALID command (i.e. non-existent msg_id) requests or try a PROTOCOL_MESSAGE_ATTRIBUTE(INVALID_command) looking for an SCMI_NOT_FOUND reply.
This is correct but there are no testcases trying to issue a VALID command against a platform where that command is unsupported: such attempts should receive back an SCMI_NOT_SUPPORTED error reply. Typical examples of this could be trying to enable notifications or using fastchannels on a platform where, respectively, notifications or fast_channels are not supported.