power: vm communication channels in guest

power: vm communication channels in guest

Allows for the opening of Virtio-Serial devices on a VM, where a DPDK
application can send packets to the host based monitor. The packet formatted is
specified in channel_commands.h
Each device appears as a serial device in path
/dev/virtio-ports/virtio.serial.port.<agent_type>.<lcore_num> where each lcore
in a DPDK application has exclusive to a device/channel.
Each channel is opened in non-blocking mode, after a successful open a test
packet is send to the host to ensure the host side is monitoring.

Signed-off-by: Alan Carew <alan.carew@intel.com>
Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>