x86: Turn the local APIC Interrupts class into a SimObject.

x86: Turn the local APIC Interrupts class into a SimObject.

It will no longer be a PioDevice or a ClockedObject, but will carry
forward the little bits and pieces of those classes that it was using.
Those are a PIO port for memory mapped register accesses, and a clock
domain parameter for setting the apic tick frequency.

This brings the x86 Interrupts class in line with the Interrupts of the
other ISAs so that they can inherit from a standard base class.

Change-Id: I6b25fa21911b39a756e0cf9408c5489a81d6ca56
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20829
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Brandon Potter <Brandon.Potter@amd.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>