net: phy: make board_phy_config responsible for calling drv->config

Boards may have things they want done before or after normal phy config.
Letting the boards call drv->config allows them more flexibilty.
Boards affected by this change are corenet_ds and mpc8544ds.

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
Acked-by: Dirk Behme <dirk.behme@de.bosch.com>