Make it clear that BIOS may modify some register settings.

Link: https://lore.kernel.org/r/1589552025-165012-3-git-send-email-john.garry@huawei.comSigned-off-by: Luo Jiaxing <luojiaxing@huawei.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>