qemu: Improve PS/2 controller detection

qemu: Improve PS/2 controller detection

Up until now, we've assumed that all x86 machines have a PS/2
controller built-in. This assumption was correct until QEMU v4.2
introduced a new x86-based machine type - microvm.

Due to this assumption, a pair of unnecessary PS/2 inputs are implicitly
added to all microvm domains. This patch fixes that by whitelisting
machine types which are known to include the i8042 PS/2 controller.

Signed-off-by: Kamil Szczęk <kamil@szczek.dev>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>