KVM: x86: Move kvm_{before,after}_interrupt() calls to vendor code

VMX can conditionally call kvm_{before,after}_interrupt() since KVM
always uses "ack interrupt on exit" and therefore explicitly handles
interrupts as opposed to blindly enabling irqs.

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