4.19/rpi4: enable kvm and disable some unneeded stuff

Closes https://git.helsinki.tools/helsinki-systems/helsinki/-/issues/135

[    1.163460] kvm [1]: 8-bit VMID
[    1.164183] kvm [1]: vgic interrupt IRQ1
[    1.164372] kvm [1]: Hyp mode initialized successfully

nixos/tests/simple.nix baut auch.