hw/sparc/sun4m: Fix problems with device introspection

hw/sparc/sun4m: Fix problems with device introspection

Several devices of the sun4m machines are using &error_fatal in
their instance_init function and thus can cause QEMU to abort
unexpectedly:

$ echo "{'execute':'qmp_capabilities'}"\
       "{'execute':'device-list-properties',"\
       " 'arguments':{'typename':'openprom'}}" \
       | sparc-softmmu/qemu-system-sparc -M SS-10 -S -qmp stdio
{"QMP": {"version": {"qemu": {"micro": 91, "minor": 11, "major": 2},
 "package": "build-all"}, "capabilities": []}}
{"return": {}}
RAMBlock "sun4m.prom" already registered, abort!
Aborted (core dumped)

$ echo "{'execute':'qmp_capabilities'}"\
       "{'execute':'device-list-properties',"\
       " 'arguments':{'typename':'macio_idreg'}}" \
       | sparc-softmmu/qemu-system-sparc -M SS-10 -S -qmp stdio
{"QMP": {"version": {"qemu": {"micro": 91, "minor": 11, "major": 2},
 "package": "build-all"}, "capabilities": []}}
{"return": {}}
RAMBlock "sun4m.idreg" already registered, abort!
Aborted (core dumped)

$ echo "{'execute':'qmp_capabilities'}"\
       "{'execute':'device-list-properties',"\
       " 'arguments':{'typename':'tcx_afx'}}" \
       | sparc-softmmu/qemu-system-sparc -M SS-5 -S -qmp stdio
{"QMP": {"version": {"qemu": {"micro": 91, "minor": 11, "major": 2},
 "package": "build-all"}, "capabilities": []}}
{"return": {}}
RAMBlock "sun4m.afx" already registered, abort!
Aborted (core dumped)

Fix the issues by converting the instance_init functions into realize()
functions instead, which are allowed to fail (and not called during
device introspection).

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>