libxc: create p2m list outside of kernel mapping if supported

libxc: create p2m list outside of kernel mapping if supported

In case the kernel of a new pv-domU indicates it is supporting a p2m
list outside the initial kernel mapping by specifying INIT_P2M, let
the domain builder allocate the memory for the p2m list from physical
guest memory only and map it to the address the kernel is expecting.

This will enable loading pv-domUs larger than 512 GB.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>