[CORE] devemu: Depricate generic methode of routing host irq to guest irq

The current generic methode of routing host irq does will not work for
old/legacy PICs which have level-triggered interrupts (for example, VIC
found in VersatilePB).

Further advanced PICs such as GICv2 implement a state machine per HW-irq
to track state of the irq. This advanced PICs may also have handshaking
methode of notifying-back HW devices about end-of-interrupts. The current
generic irq routing methode enables/disables host irq which can spoil the
internal state of HW-irq in advanced PIC.

I have been discussing our current methode of routing host irq to guest
irq with some of few HW designers. They also agree with above described
short-comings of our generic irq routing.

This patch depricates our generic methode of routing host irq to guest irq.

Please note that we are not depricating pass-through device support. We
will still support pass-through devices using HW-assisted PIC emulators.

We will rely on HW-assisted PIC emulators (such as VGIC) to provided host
irq to guest irq routing since irq routing cannot be implemented by simply
enabling/disabling host irq lines.

Signed-off-by: Anup Patel <anup@brainfault.org>