phylib: Enable AR8021 phy support

Enable AR8021 as it used on Freescale boards: P1020RDB-PC, P1021RDB-PC,
P2020RDB-PC, P1020UTM-PC, and P1020MSBG-PC.

Signed-off-by: Xie Xiaobo <X.Xie@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>