hw/timer/mc146818rtc: Fix introspection problem

hw/timer/mc146818rtc: Fix introspection problem

There is currently a funny problem with the "mc146818rtc" device:
1) Start QEMU like this:
   qemu-system-ppc64 -M pseries -S
2) At the HMP monitor, enter "info qom-tree". Note that there is an
   entry for "/rtc (spapr-rtc)".
3) Introspect the mc146818rtc device like this:
   device_add mc146818rtc,help
4) Run "info qom-tree" again. The "/rtc" entry is gone now!

The rtc_finalize() function of the mc146818rtc device has two bugs: First,
it tries to remove a "rtc" property, while the rtc_realizefn() added a
"rtc-time" property instead. And second, it should have been done in an
unrealize function, not in a finalize function, to avoid that this causes
problems during introspection.

But since adding aliases to the global machine state should not be done
from a device's realize function anyway, let's rather fix this issue
by moving the creation of the alias to the code that creates the device
(and thus is run from the machine init functions instead), i.e. the
mc146818_rtc_init() function for most machines. The prep machines are
special, since the mc146818rtc device is created here in the realize
function of the i82378 device. Since we certainly don't want to add the
alias there, we add it to some code that is called from the ibm_40p_init()
machine init function instead.
Since the alias is now only created during the machine init, we can remove
the object_property_del() completely.

Fixes: 654a36d857ff949e0d1989904b76f53fded9dc83
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1534419358-10932-5-git-send-email-thuth@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>