Set NRIPS in KVM capabilities if and only if nrips=true, which naturally
incorporates the boot_cpu_has() check, and set nrips_enabled only if the
KVM capability is enabled.

Note, previously KVM would set nrips_enabled based purely on userspace
input, but at worst that would cause KVM to propagate garbage into L1,
i.e. userspace would simply be hosing its VM.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>