TI: OMAP3: Overo Tobi ethernet support

Add setup for ethernet on Tobi, allowing kernel/ramdisk to be loaded
over tftp.

This also refactors the smc911x driver to allow for detecting when the
chip is missing. I.e. the detect_chip() function is called earlier and
will abort gracefully when the Chip ID read returns all 1's.

Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Dirk Behme <dirk.behme@googlemail.com>
Acked-by: Ben Warren <biggerbadderben@gmail.com>