KVM: selftests: Use this_cpu_has() to detect SVM support in L1

Replace an evil open coded instance of querying CPUID from L1 with
this_cpu_has(X86_FEATURE_SVM).

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-35-seanjc@google.com