pasemi_mac: Abstract out register access

Abstract out the PCI config read/write accesses into reg read/write ones,
still calling the pci accessors on the back end.

Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: David S. Miller <davem@davemloft.net>