Allow -serial chardev:<name>

Allow -serial chardev:<name>

Lets put -chardev into use now.  With this patch applied chardev:name is
accepted as chardev specification everywhere, i.e. now you can:

	-chardev stdio,id=ttyS0
	-serial chardev:ttyS0

which does the same as '-serial stdio".

Muxing can be done this way:

	-chardev stdio,id=mux,mux=on
	-serial chardev:mux
	-monitor chardev:mux

You can mux more than two streams.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>