Add support for named virtio console ports

[jceel]

Summary

Following change adds support for named ports in the virtio_console(4) driver. It does that by creating tty aliases in format /dev/vtcon/<portname> upon receiving PORT_NAME event (id = 7) over the control queue. The aliases point to already existing /dev/ttyVx.y tty device nodes.

Test Plan

Code can be tested using qemu-kvm in linux: https://fedoraproject.org/wiki/Features/VirtioSerial

[jceel]

Port names are not null-terminated - putting '\0' at the last byte was wrong.