configs: imx6-engicam: Drop fec phy address and mode

Now all the fec related phy properties are now accessible
via dts. So drop the explicit config items from common
config file, imx6-engicam.h

Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>