qdev: Use GList for global properties

If the same GlobalProperty struct is registered twice, the list
entry gets corrupted, making tqe_next points to itself, and
qdev_prop_set_globals() gets stuck in a loop. The bug can be
easily reproduced by running:

  $ qemu-system-x86_64 -rtc-td-hack -rtc-td-hack

Change global_props to use GList instead of queue.h, making the
code simpler and able to deal with properties being registered
twice.

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
