net: hns3: split hclge_reset() into preparing and rebuilding part

hclge_reset() is a little bloated, and the process of PF FLR will
be separated from the reset task later. So this patch splits
hclge_reset() into hclge_reset_prepare() and hclge_reset_rebuild(),
then FLR can also reuse these two functions.

BTW, since hclge_clear_reset_cause() and hclge_reset_prepare_up()
will not affect the device, so in hclge_reset_rebuild(), these
functions are called without rtnl_lock.

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