fix #1908: add vmgenid config/device

fix #1908: add vmgenid config/device

this adds a VM Generation ID device uses by Windows (Server) to determine
some specific actions that may have happened with the vm
such as rollback, restore, etc.

see:

https://docs.microsoft.com/en-us/windows/desktop/hyperv_v2/virtual-machine-generation-identifier

for details on how it works and when it should change

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>