FROMLIST: cfi: free old cfi shadow asynchronously

Currenly, it uses synchronize_rcu() to wait old rcu reader to go away
in update_shadow.In embedded platform like ARM CA7X,
load_module blocks 40~50ms in update_shadow.
When there are more than one hundred kernel modules,
it blocks several seconds.

To accelerate load_module,change synchronize_rcu to call_rcu.

Change-Id: I08dcb29ef97453b836efd0d64286196600be8cce
Signed-off-by: Haibo Li <haibo.li@mediatek.com>
Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
Link: https://lore.kernel.org/lkml/20220704014046.34596-3-haibo.li@mediatek.com/


Bug: 236922027
Bug: 257362811
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>