x86/kvm/svm: Simplify cpu_has_svm()

Use already cached CPUID information instead of querying CPUID again.

No functionality change.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: kvm@vger.kernel.org
Cc: x86@kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>