target-unicore32: Mark as unmigratable

target-unicore32: Mark as unmigratable

CPU_SAVE_VERSION 2 was bogus as both save and load would just throw a
hw_error(). Therefore we can without problems suppress registration of
"cpu_common" VMState by dropping CPU_SAVE_VERSION define and provide an
unmigratable "cpu" VMStateDescription for UniCore32CPU at device level
instead, where we can attach this the QOM way.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Juan Quintela <quintela@redhat.com>