tsec: Add support for using the BCM5482 PHY in fiber mode

The BCM5482 PHY supports both copper and fiber as an ethernet medium.
By enabling its copper/fiber mode auto-detection feature it can
dynamically determine if it should be configured for copper or fiber.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>