extcon: Add stubs for extcon_register_notifier_all() functions

stable inclusion
from stable-5.10.28
commit 023d13952e9b7479e60d79098a7dcc82276ea315
bugzilla: 51779

--------------------------------

[ Upstream commit c9570d4a ]

Add stubs for extcon_register_notifier_all() function for !CONFIG_EXTCON
case.  This is useful for compile testing and for drivers which use
EXTCON but do not require it (therefore do not depend on CONFIG_EXTCON).

Fixes: 815429b3 ("extcon: Add new extcon_register_notifier_all() to monitor all external connectors")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by:   Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>