[Skiboot] OpenPower gard tool rework

[Oliver O'Halloran]

Hi,

This series contains a substantial rework of the OpenPower gard tool.
The main additions being:

	a) The ability to create GARD records
	b) Support for Power 9
	c) Support for running on ARM (i.e BMCs)
	d) Nicer output for the list subcommand.
	e) A basic understanding of where to find GUARD on OpenBMC
           with vPNOR.

This also does substantial (but incomplete) reworks of the internals of the
tool to make it a bit easier to work with.

Record creation has only been lightly tested, but it seems to work
provided the user targets a hardware unit that actually exists which
is good enough for me.

Oliver