kvmconfig: add more virtio drivers

"make defconfig kvmconfig" is supposed to end up with usable kernel for
KVM guest. In practice, it won't work for e.g. Hetzner VPS (KVM-based)
unless you add these options.

Signed-off-by: Andrey Utkin <andrey_utkin@fastmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>