Switch to use hypervisor_cpuid_base() to detect KVM.

Cc: Gleb Natapov <gleb@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: http://lkml.kernel.org/r/1374742475-2485-3-git-send-email-jasowang@redhat.comSigned-off-by: H. Peter Anvin <hpa@linux.intel.com>