pvh dom0: construct_dom0 changes

pvh dom0: construct_dom0 changes

This patch changes construct_dom0() to boot in pvh mode:
  - Make sure dom0 elf supports pvh mode.
  - Call guest_physmap_add_page for pvh rather than simple p2m setting
  - Map all non-RAM regions 1:1 upto the end region in e820 or 4GB which
    ever is higher.
  - Allocate p2m, copying calculation from toolstack.
  - Allocate shared info page from the virtual space so that dom0 PT
    can be updated. Then update p2m for it with the actual mfn.
  - Since we build the page tables for pvh same as for pv, in
    pvh_fixup_page_tables_for_hap we replace the mfns with pfns.

Signed-off-by: Mukesh Rathor <mukesh.rathor@oracle.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>