cfg2cmd: disable SMM when display=none and SeaBIOS is both used

cfg2cmd: disable SMM when display=none and SeaBIOS is both used

issue reported in community forum [0][1], like "serial[n]" display we
also need to set this option for "none", otherwise we get a boot
loop.

[0]: https://forum.proxmox.com/threads/99508
[1]: https://forum.proxmox.com/threads/97310/post-427129

Signed-off-by: Oguz Bektas <o.bektas@proxmox.com>
Reviewed-by: Fabian Ebner <f.ebner@proxmox.com>
Tested-by: Fabian Ebner <f.ebner@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>