net: phy: icplus: Use the RGMII interface mode to configure clock delays

Like several other PHY devices which support RGMII, the IC+1001 allows
additional delays to by added to the RX_CLK and TX_CLK signals to
compensate for skew between the clock and data signals. Previously this
was always enabled, but this change makes use of the different RGMII
interface modes to allow the user to specify whether this should be
enabled.

Signed-off-by: Stuart Menefy <stuart.menefy@st.com>
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>