core: Virtualize legacy MSI for interrupt remapping support

core: Virtualize legacy MSI for interrupt remapping support

Analogously to edge-triggered IOAPIC interrupts, handover all legacy
MSIs by disabling them first, programming the VT-d remapping table and
then writing remappable parameters into the MSI capability registers.
An additional triggering of active vectors ensures that we do not lose
events during handover.

Disabling is done on x86 via a trick: we program an empty CPU mask in
logical destination mode.

MSI-X remains on the to-do list. Thus, once enabling interrupt
remapping, systems that use MSI-X will become unsupported for the time
being.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>