documentation: remove references to cpu_*_map.

This has been obsolescent for a while, fix documentation and
misc comments.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index b132ade..4f51beb 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -967,7 +967,7 @@
 	xen_setup_mfn_list_list();
 }
 
-/* This is called once we have the cpu_possible_map */
+/* This is called once we have the cpu_possible_mask */
 void xen_setup_vcpu_info_placement(void)
 {
 	int cpu;