83xx: UEC: Added support for bitBang MII driver access to PHYs

This patch enabled support for having PHYs on bitBang MII and uec MII
operating at the same time. Modeled after the MPC8360ADS implementation.

Added the ability to specify which ethernet interfaces have bitbang SMI
on the board header file.

Signed-off-by: Richard Retanubun <RichardRetanubun@RuggedCom.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>