add virtio-console cmdline option (Christian Ehrhardt)

This patch adds the typical qemu console command line switch to the virtio
console. using -virtioconsole ARG it can now be specified what output a guest
hvc should be redirected to.

Signed-off-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6317 c046a42c-6fe2-441c-8c8c-71466251a162