netxen: separate register and memory access lock

Since register and onboard memory access has separate
window registers, they need not be kept under same lock.

Also, memory is always accessed from process context
(mostly for firmware init and diagnostic tools).

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