pseries: phyp dump: hypervisor-assisted dump

The following series of patches implement a basic framework for hypervisor-assisted dump. The very first patch provides
documentation explaining what this is :-) . Yes, its supposed
to be an improvement over kdump.

A list of open issues / todo list is included in the documentation. It also appears that the not-yet-released firmware versions this was tested on are still, ahem, incomplete; this work is also pending.

I have included most of the changes requested. Although, I did find one or two, fixed in a later patch file rather than the first location they appeared at.

-- Manish & Linas.