KVM: x86: Check for Intel PT MSR virtualization using KVM cpu caps

Use kvm_cpu_cap_has() to check for Intel PT when processing the list of
virtualized MSRs to pave the way toward removing ->pt_supported().

No functional change intended.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>