libqemustub: add stubs to be able to use qemu-char.c

libqemustub: add stubs to be able to use qemu-char.c

chardev depends on lots of external symbols that are not necessarily
needed to be able to use, for example, 'socket chardev'. So add stubs
for these functions:

 - bdrv_commit_all
 - qemu_chr_open_msmouse
 - is_daemonized
 - qemu_add_machine_init_done_notifier
 - monitor_init
 - qemu_notify_event
 - vc_init

and this array:

 - serial_hds

Signed-off-by: Antonios Motakis <a.motakis@virtualopensystems.com>
Signed-off-by: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>