migration: Add Error** argument to .save_setup() handler

migration: Add Error** argument to .save_setup() handler

The purpose is to record a potential error in the migration stream if
qemu_savevm_state_setup() fails. Most of the current .save_setup()
handlers can be modified to use the Error argument instead of managing
their own and calling locally error_report().

Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Harsh Prateek Bora <harshpb@linux.ibm.com>
Cc: Halil Pasic <pasic@linux.ibm.com>
Cc: Thomas Huth <thuth@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Cc: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Cc: John Snow <jsnow@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/r/20240320064911.545001-8-clg@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>