Please add KVM support to salsa runners (for autopkgtests)

Autopkgtests can take advantage of KVM support in DebCI runners, but AFAIK not on salsa CI. Would it be possible to add KVM support there too?

Rationale: In order to test unlocking at early boot stage for cryptsetup (and also dropbear-initramfs) we have autopkgtests that start QEMU and mock user interaction through the serial console. With KVM acceleration the test takes ~1min to complete; without KVM it takes ~30min so one can't test more than a handful partitioning layouts.

On DebCI /dev/kvm isn't exposed to autopkgtest, but (some?) runners do support it and the device file can be created with mknod /dev/kvm c 10 232 so QEMU can take advantage of hardware acceleration. AFAICT the same trick doesn't work on salsa CI runners as /proc/cpuinfo appears to lack virtualization instructions. Presumably the host actually does have KVM support, but currently doesn't expose the capability to salsa runners.