When udev is installed (and scheduled to be started), but not running
yet, plain dmsetup will deadlock on waiting for udev. Since we call
`dmsetup mknodes dmroot` anyway
QubesOS/qubes-issues#1354
When PV Grub will be used, VM initramfs should not contain /lib/modules
mounting code, as the VM root.img will already contains kernel modules.
Make it possible by splitting the module.
QubesOS/qubes-issues#1354