xen/pvh: Add memory map pointer to hvm_start_info struct

The start info structure that is defined as part of the x86/HVM direct boot
ABI and used for starting Xen PVH guests would be more versatile if it also
included a way to pass information about the memory map to the guest. This
would allow KVM guests to share the same entry point.

Signed-off-by: Maran Wilson <maran.wilson@oracle.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>