KVM: selftests: Use kvm_cpu_has() for nSVM soft INT injection test

Use kvm_cpu_has() to query for NRIPS support instead of open coding
equivalent functionality using kvm_get_supported_cpuid_entry().

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-16-seanjc@google.com