x86/xen: rename some PV-only functions in smp_pv.c

After code split between PV and HVM some functions in xen_smp_ops have
xen_pv_ prefix and some only xen_ which makes them look like they're
common for both PV and HVM while they're not. Rename all the rest to
have xen_pv_ prefix.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>