lxd/instance/qemu: Cleanup VGA ROM check
lxd/instance/qemu: Cleanup VGA ROM check

This switches to using a checker function and adds a check for SR-IOV
VFs where messing with the VGA firmware apparently crashes QEMU.

Those cards don't have physical outputs so the VGA firmware is likely an
afterthought.

Signed-off-by: Stéphane Graber <089afc6d81f66f1168a9849e15660feae286e024@ubuntu.com>

hallyn/lxd,lxc/lxd,hallyn/lxd,atxwebs/lxd,stgraber/lxd,hallyn/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,lxc/lxd,atxwebs/lxd,hallyn/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,atxwebs/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,hallyn/lxd,stgraber/lxd,atxwebs/lxd,lxc/lxd,stgraber/lxd