CH 8 doesn't boot install media on Ryzen APUs

References:
https://github.com/xcp-ng/xcp/issues/206
https://xcp-ng.org/forum/topic/1370/xcp-ng-8-0-0-beta-now-available/90
https://forum.opsi.org/viewtopic.php?f=8&t=10611
Et al.

In short: Several recent kernel versions seem to have a bug affecting Ryzen APUs:
If memory is not limited (tested successfully with 2048M), installmedia willf freeze.

Reproducable with every AMD Ryzen APU (probably limited to APU, not CPU!)

We know that Ryzen APUs are no supported platform, but for compatibility reasons and because of the lower limit (current is 8192M) shouldn't have any effect for the installer...