inmates: Add IOAPIC demo

Simply demonstration and test for using the IOAPIC within an non-root
cell: Rob the ACPI IRQ and wait for events on this line, e.g. a power
button push. Read the warning before using it.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
inmates: Halt on return from inmate_main

Remove the need for explicit clt;hlt from the inmates, moving this to
header code.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
inmates: Add primitive 32-bit demo

This only demonstrates the capability to build inmates which come up in
32-bit mode. Note that not all library services support this already.

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