net/phy: fix select line for TN80xx

net/phy: fix select line for TN80xx

TN80xx has same PHY ID as TN2020, but it needs different setting to register
30.93 which used to select line, so we read register 30.32 which has
bit 15:12 to indicate PHY hardware version, for TN20xx we will get 3 or 2,
for TN80xx we will get 5 or 4.

Signed-off-by: Shaohui Xie <Shaohui.Xie@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>