xen: save linear p2m list address in shared info structure

The virtual address of the linear p2m list should be stored in the
shared info structure read by the Xen tools to be able to support
64 bit pv-domains larger than 512 GB. Additionally the linear p2m
list interface includes a generation count which is changed prior
to and after each mapping change of the p2m list. Reading the
generation count the Xen tools can detect changes of the mappings
and re-read the p2m list eventually.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Konrad Rzeszutek Wilk <Konrad.wilk@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>