kvm: Resolve missing-field-initializers warnings

Resolve missing-field-initializers warnings seen in W=2 kernel
builds by having macros generate more elaborated initializers.
That is enough to silence the warnings.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>