cfg2cmd: vga: fix #2749: disable edid for Win+BIOS+VGA machines

cfg2cmd: vga: fix #2749: disable edid for Win+BIOS+VGA machines

Edid support was added with Qemu 5. Windows guests seem to not be able
to get all possible resolutions if the default std VGA device is used as
GPU and the VM boots in BIOS mode. The result is that only one of the
following three resolutions can be configured:

800x600
1024x768
1920x1080

It is important to note that just booting a Windows VM with the edid=off
parameter will not make the large list of resolutions available. It
seems that Windows is caching the list of possible resolutions
somewhere [0].

Uninstalling the 'Microsoft Basic Display Adapter' in the device manager
and rebooting the VM is one way I found to force Windows to recreate the
list of possible resolutions.

Signed-off-by: Aaron Lauterer <a.lauterer@proxmox.com>
[0] https://lists.nongnu.org/archive/html/qemu-devel/2020-07/msg07128.html