qom: Replace object property list with GHashTable

ARM GICv3 systems with large number of CPUs create lots of IRQ pins. Since
every pin is represented as a property, number of these properties becomes
very large. Every property add first makes sure there's no duplicates.
Traversing the list becomes very slow, therefore QEMU initialization takes
significant time (several seconds for e. g. 16 CPUs).

This patch replaces list with GHashTable, making lookup very fast. The only
drawback is that object_child_foreach() and object_child_foreach_recursive()
cannot add or remove properties during traversal, since GHashTableIter does
not have modify-safe version. However, the code seems not to modify objects
via these functions.

Signed-off-by: Pavel Fedin <p.fedin@samsung.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Tested-by: Pavel Fedin <p.fedin@samsung.com>
[AF: Fixed object_property_del_{all,child}() issues;
     g_hash_table_contains() -> g_hash_table_lookup(), suggested by Daniel]
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
