This can be used to set machine options like highmem=off for running old
armvirt/32 kernel lacking LPAE support with QEMU version 3.0 or later
[1] Armv7 guest fails to boot with qemu-3.0.0-1,
https://bugzilla.redhat.com/show_bug.cgi?id=1633328#c5
Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>