!941 LoongArch: fix 2k500 sfb driver not work during reboot

Merge Pull Request from: @Hongchen_Zhang 
 
LS7A Root Ports have a hardware defect: clearing PCI_COMMAND_MASTER *also*
prevents the bridge from forwarding CPU MMIO requests in the downstream
direction, and these MMIO accesses to devices below the bridge happen even
after .shutdown(), e.g., to print console messages.  LS7A neither forwards
the requests nor sends an unsuccessful completion to the CPU, so the CPU
waits forever, resulting in the hang.

After apply this PR,the machine which has 2k500 bmc connected to the LS7A bridge can reboot normally. 
 
Link:https://gitee.com/openeuler/kernel/pulls/941

 

Reviewed-by: Guo Dongtai <guodongtai@kylinos.cn>
Reviewed-by: Jialin Zhang <zhangjialin11@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>