sis900: stop using net_device.{base_addr, irq} and convert to __iomem.

- pci_resource_start() can be removed from sis900_get_mac_addr() because
  the IO range is maped and stored into the device private struct early
  in the device probe function.
- the driver contains a few direct accesses to low IO ports that forbid
  to re(#)define the usual out{l, w, b} macros.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Daniele Venzano <venza@brownhat.org>