r8169: factor out redundant RTL8168d PHY config functionality to rtl8168d_1_common()

rtl8168d_2_hw_phy_config() shares quite some functionality with
rtl8168d_1_hw_phy_config(), so let's factor out the common part to a
new function rtl8168d_1_common(). In addition improve the code a little.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>