vmd(8): stop toggling irq deassert for edge triggered devs.

vmd(8): stop toggling irq deassert for edge triggered devs.

For edge-triggered devices, there's no need to deassert an irq given
how vmd(8) emulates a pic.  Deassertion grabs a lock and can trigger
the ioctl for toggling pending interrupts causing a race condition.
This results in a storm of vm-exits and guest vcpu becoming
unresponsive.

The original sign of this issue is guest "pauses" when pasting text
into a serial console connection in something like xterm(1).

Tested by mbuhl@, cheloha@, sashan@, kn@, and mlarkin@.

"go for it", mlarkin@