KVM: x86: Move triple fault request into RM int injection

Request triple fault in kvm_inject_realmode_interrupt() instead of
returning EMULATE_FAIL and deferring to the caller.  All existing
callers request triple fault and it's highly unlikely Real Mode is
going to acquire new features.  While this consolidates a small amount
of code, the real goal is to remove the last reference to EMULATE_FAIL.

No functional change intended.

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