can: add driver for Softing card

This patch adds a driver for the platform:softing device.
This will create (up to) 2 CAN network devices from 1
platform:softing device

Signed-off-by: Kurt Van Dijck <kurt.van.dijck@eia.be>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: David S. Miller <davem@davemloft.net>