Add wctablet device

Add QEMU Wacom Penpartner serial tablet emulation.
GSoC 2016 project.

Signed-off-by: Anatoli Huseu1 <avg.tolik@gmail.com>

Various cleanups.
Add line speed tracking.
Implement ST and SP commands.
Adapted to chardev QOMification.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1486391007-10116-1-git-send-email-kraxel@redhat.com