net: sunhme: Consolidate mac address initialization

The mac address initialization is braodly the same between PCI and SBUS,
and one was clearly copied from the other. Consolidate them. We still have
to have some ifdefs because pci_(un)map_rom is only implemented for PCI,
and idprom is only implemented for SPARC.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>