IOC mediator: add IOC channel operations

IOC mediator communicates with native IOC HW through several native channels of
CBC protocol. And IOC mediator communicates with virtual UART through one virtual
channel.

This patch implements channel operations including open/close/read/write.

Signed-off-by: Liu Yuan <yuan1.liu@intel.com>
Reviewed-by: Wang Yu <yu1.wang@intel.com>
Reviewed-by: Liu Shuo <shuo.a.liu@intel.com>
Reviewed-by: Zhao Yakui <yakui.zhao@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

Author: yliu80