netxen: onchip memory access change

Add support for different windowing scheme for on chip
memory in future chip revisions. This is required by
diagnostic tools.

Signed-off-by: Amit Kumar Salecha <amit@netxen.com>
Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: David S. Miller <davem@davemloft.net>