[RFC] P9 ldmx support

[Michael Neuling]

> Re: [RFC] P9 ldmx support

These are good to go and don't need to be marked as RFC.

FWIW, we've been testing these internally and they've been solid.

> These are patches based on next to support the forthcoming ldmx
> instruction through the existing P8 EBB infrastructure. Obviously it
> doesn't actually *work* without some other patches and a P9 system,
> but with the context switch change to FSCR it makes sense to get
> this upstream for testing ASAP.

Yep.

Thanks,
Mikey

> The first patch context switches FSCR per thread so that the second patch can
> lazily enable this feature (FSCR.LM) with a facility unavailable exception
> and context switch two new ldmx registers (LMRR / LMSER) per thread as well.
> Third patch is a couple of basic tests.