Now we got two classes: IdeChannel and MacioIdeChannel.
The former models a generic IDE channel so it can be used elsewhere.
The latter implements MacIO specific configuration register(s)
and interrupt signaling.
Result of running IWYU (https://include-what-you-use.org/) and
applying most of the suggestions about unncessary includes and
forward declarations.
Was motivated by observing that <thread> was being included in
ppcopcodes.cpp even though it was unused (found while researching
the use of threads), but seems generally good to help with build
times and correctness.
