m68k: defconfig: Enable ATARI_SVETHLANA and ETHOC

Enable support for the SVEthLANa network adapter built into the
SuperVidel CT60 FPGA extension, which is compatible with OpenCores
10/100 Mbps Ethernet.

SVEthLANa works fine with phylib's Generic PHY fallback, so there is no
need to enable any PHY drivers.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://patch.msgid.link/42db3dfd79c69a95475b3b187437efcc162dfbff.1790514278.git.geert@linux-m68k.org