Issue a full soft reset at probe time.

This was reported by Doong Ping of Micrel, but no explanation of why this
is necessary or what bug it is fixing. Add it as it does not seem to hurt
the current driver and ensures that the device is in a known state when we
start setting it up.
Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>