SMC911X: Add chip auto detection

Refactor 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>