xen/pvh: Do not fill kernel's e820 map in init_pvh_bootparams()

e820 map is updated with information from the zeropage (i.e. pvh_bootparams)
by default_machine_specific_memory_setup(). With the way things are done
now,  we end up with a duplicated e820 map.

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