KVM: Fix references to non-existent KVM_CAP_TRIPLE_FAULT_EVENT

The x86-only KVM_CAP_TRIPLE_FAULT_EVENT was (appropriately) renamed to
KVM_CAP_X86_TRIPLE_FAULT_EVENT when the patches were applied, but the
docs and selftests got left behind.  Fix them.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>