Besides the altcall conversion, some further adjustments appeared desirable
to do while touching that area.

1: IOMMU/x86: switch to alternatives-call patching in further instances
2: VT-d / x86: re-arrange cache syncing
3: VT-d: replace flush_all_cache()
4: IOMMU/PCI: propagate get_device_group_id() failure

I'm sending this v2 after waiting for quite some time on continuing some
aspects which were discussed on the v1 thread, but no luck. Also there's
a new 4th patch now, as kind of a result from on part of that discussion.

Jan