KVM: x86: don't notify userspace IOAPIC on edge EOI

On real hardware, edge-triggered interrupts don't set a bit in TMR,
which means that IOAPIC isn't notified on EOI.  Do the same here.

Staying in guest/kernel mode after edge EOI is what we want for most
devices.  If some bugs could be nicely worked around with edge EOI
notifications, we should invest in a better interface.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>