dev: Generalize the x86 int source/sink pins.

Sink pins are now templated based on the underlying device types, and
the pins themselves are based on the new, generalized Port mechanism.

Change-Id: I09c678c56f6eb6b4a167c12f221ae0241fe99c2d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20700
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>