kvm: x86: Add payload operands to kvm_multiple_exception

kvm_multiple_exception now takes two additional operands: has_payload
and payload, so that updates to CR2 (and DR6 under VMX) can be delayed
until the exception is delivered. This is necessary to properly
emulate VMX or SVM hardware behavior for nested virtualization.

The new behavior is triggered by
vcpu->kvm->arch.exception_payload_enabled, which will (later) be set
by a new per-VM capability, KVM_CAP_EXCEPTION_PAYLOAD.

Reported-by: Jim Mattson <jmattson@google.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>