tsec: Fix eTSEC2 link problem on P2020RDB

On P2020RDB eTSEC2 is connected to Vitesse VSC8221 PHY via SGMII.
Current TBI PHY settings for SGMII mode cause link problems on
this platform, link never comes up.

Fix this by making TBI PHY settings configurable and add a working
configuration for P2020RDB.

Signed-off-by: Felix Radensky <felix@embedded-sol.com>
Acked-by: Andy Fleming <afleming@freescale.com>