net: hns3: refactor the notification scheme of PF reset

hclge_reset_prepare_down() is only used to inform VF that PF is
going to do function reset, then using hclge_func_reset_sync_vf()
in hclge_reset_prepare_wait() to query whether VF is ready before
asserting PF function reset. To make the code more readable,
this patch uses a new function hclge_function_reset_notify_vf()
to do this job.

Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>