certs: Move load_system_certificate_list to a common function

stable inclusion
from stable-5.10.47
commit 72d6f5d982f0e823eaa01b9439db23af85fb0ee0
bugzilla: 172973 https://gitee.com/openeuler/kernel/issues/I4DAKB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=72d6f5d982f0e823eaa01b9439db23af85fb0ee0



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

[ Upstream commit 2565ca7f ]

Move functionality within load_system_certificate_list to a common
function, so it can be reused in the future.

DH Changes:
 - Added inclusion of common.h to common.c (Eric [1]).

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: keyrings@vger.kernel.org
Link: https://lore.kernel.org/r/EDA280F9-F72D-4181-93C7-CDBE95976FF7@oracle.com/ [1]
Link: https://lore.kernel.org/r/20200930201508.35113-2-eric.snowberg@oracle.com/
Link: https://lore.kernel.org/r/20210122181054.32635-3-eric.snowberg@oracle.com/ # v5
Link: https://lore.kernel.org/r/161428672825.677100.7545516389752262918.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/161433311696.902181.3599366124784670368.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161529605850.163428.7786675680201528556.stgit@warthog.procyon.org.uk/

 # v3
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: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>