qemu: Install *microvm* machine type

[pmenzel]

From ‘microvm’ virtual platform (microvm):

microvm is a machine type inspired by Firecracker and constructed after its machine model.

It’s a minimalist machine type without PCI nor ACPI support, designed for short-lived guests. microvm also establishes a baseline for benchmarking and optimizing both QEMU and guest operating systems, since it is optimized for both boot time and footprint.

[pmenzel]

It’s already build by default:

qemu-system-x86_64 -M microvm -kernel /boot/mariux.375 -append "console=ttyS0,115200" -serial stdio …