Revert "net: phy: marvell: avoid pause mode on SGMII-to-Copper for 88e151x"

This reverts commit 6623c0fb.

The original diagnosis was incorrect: it appears that the NIC had
PHY polling mode enabled, which meant that it overwrote the PHYs
advertisement register during negotiation.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Tested-by: Yonglong Liu <liuyonglong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>