net: smc91x: Add Atari EtherNAT support

Add Atari specific code to the smc91x Ethernet driver. This code is used
on the EtherNAT adapter card for the Atari Falcon extension port.

Signed-off-by: Michael Schmitz <schmitz@debian.org>
Tested-by: Christian Steigies <cts@debian.org>
[geert: Sort Kconfig entries, split in hard and soft dependencies]
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: David S. Miller <davem@davemloft.net>