fix #4620: cfg2cmd: drive device: correctly handle IDE for q35

fix #4620: cfg2cmd: drive device: correctly handle IDE for q35

Only unit 0 for IDE is supported with machine type q35. Currently,
QEMU will fail startup with machine type q35 with an error like
> Can't create IDE unit 1, bus supports only 1 units
when ide1 or ide3 is configured.

Make sure to keep backwards compat form migration by leaving ide0 and
ide2 fixed. Since starting with ide1 or ide3 never worked, they can be
moved to a controller with a higher ID without issue.

Reported in the community forum:
https://forum.proxmox.com/threads/124615/post-543127
https://forum.proxmox.com/threads/130815/

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>