at86rf230: remove is212 and add driver data

This patch adds a new at86rf2xx_chip_data structure which holds device
specific attributes. Instead of runtime decisions "if (is212())" we set
callbacks/attributes while device detection.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>