Booting dom0, various issues since v3.16 kernels

[Stefan Bader <stefan@krikkit.de>]

Hey David,

after just being in that pain, I thought I might as well give a summary to
you/the list. Maybe helpful to not forget which piece should go to which stable...

So:
v3.16...v3.17.8: Somewhen in between those, the acpi irq seems to have broken.
                 I have not yet verified that, but at least three changes in
                 3.19-rc6 seem to look related:

 * "x86/xen: Treat SCI interrupt as normal GSI interrupt",
 * "ACPI: pci: Do not clear pci_dev->irq in acpi_pci_irq_disable()", and
 * "x86/xen: Override ACPI IRQ management callback __acpi_unregister_gsi"

v3.17.8...v3.18.4: Beside the acpi interrupt, no USB devices (beyond the
                   hubs) get initialized. Not sure what fixed it, but it
                   looks ok in v3.19-rc7.
                   Beside that, there also was a regression in swiotlb
                   that I think was passed on to some stable maintainers:

 * "Revert "swiotlb-xen: pass dev_addr to swiotlb_tbl_unmap_single""

v3.18.4..v3.19-rc7: The issues above look to be fixed. Only some Haswell
                    based box now crashed on boot as dom0 while parsing
                    some ACPI tables (will send more detail seperately).
                    This happens only on that host and only when running
                    as dom0. Bare-metal is ok and an Opteron based different
                    host is also fine.

-Stefan