[Linaro-acpi] [RFC] additional editing for arm-acpi.txt

So. What do you think of this version? I've tried to fill out some areas, clean up some others -- and it probably needs more. At one point, I broke this into a bunch of individual files, which made it easier to edit, but it does not flow very smoothly. Let me know if a bunch of small files would be preferred.

Hanjun already got most of the edits from the commentary on list; this version is mostly trying to add more content...