netxen: remove sub 64-bit mem accesses

Sub 64-bit / unaligned access to oncard memory was only used
by old diagnostic tools, causes some intermittent issues when
memory controller agent is used.  The new access method was
added by commit ea6828b8
("netxen: improve pci memory access").  Firmware init anyway
uses 8-byte strides.

This also fixes address/offset calculation for NX2031 context
memory (SIU). For NX3031, SIU uses same register offsets
as packet memory (MIU).

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>