net: phy: Add dts support for Motorcomm yt8531s gigabit ethernet phy

Add dts support for Motorcomm yt8531s gigabit ethernet phy.
 Change yt8521_probe to support clk config of yt8531s. Becase
 yt8521_probe does the things which yt8531s is needed, so
 removed yt8531s function.
 This patch has been verified on AM335x platform with yt8531s board.

Signed-off-by: Frank Sae <Frank.Sae@motor-comm.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>