xenstore: setup xenstore stubdom console interface properly

xenstore: setup xenstore stubdom console interface properly

In order to be able to get access to the console of Xenstore stubdom
we need an appropriate granttab entry. So call xc_dom_gnttab_init()
when constructing the domain and preset some information needed
for that function in the dom structure.

We need to create the event channel for the console, too. Do that and
store all necessary data locally.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wl@xen.org>