General start-of-day cleanups, resulting in the

General start-of-day cleanups, resulting in the
x86/32 map_domain_page() mapcache now being per-domain
rather than global.

Other cleanups include removal of static definition of
CPU0's idle domain. Instead a single, multi-cpu, idle domain
is dynamically created early during bootstrap.

Signed-off-by: Keir Fraser <keir@xensource.com>