char: clean up remaining chardevs when leaving

This helps to remove various chardev resources leaks when leaving qemu.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <1466105332-10285-2-git-send-email-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
