net: hns3: enable/disable ring in the enet while doing UP/DOWN

While hardware gets into reset status, the firmware will not respond to
driver's command request, which may cause ring not disabled problem
during reset process.

So this patch uses register instead of command to enable/disable the ring
in the enet while doing UP/DOWN operation.

Also, HNS3_RING_RX_VM_REG is previously unused, so change it to the
correct meaning, and add a wrapper function for readl().

Fixes: 46a3df9f

 ("net: hns3: Add HNS3 Acceleration Engine & Compatibility Layer Support")
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>