x86/shadow: adjust callback arrays

x86/shadow: adjust callback arrays

Some of them have entries with stale comments. Rather than correcting
these comments, re-arrange how these arrays get populated: Use dedicated
element initializers, serving the purpose of what the comments did so
far. This then also makes these arrays independent of the actual
ordering of the individual SH_type_*.

While tightening respective ASSERT()s in hash_{vcpu,domain}_foreach(),
also tighten related ones in shadow_hash_{insert,delete}().

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>