In some case, when mac enable|disable and adjust link, may cause hard to
link(or abnormal) between mac and phy. This patch adds the code for rx PCS
to avoid this bug.

Disable the rx PCS when driver disable the gmac, and enable the rx PCS
when driver enable the mac.
Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>