x86: Add support for IOAPIC access control

x86: Add support for IOAPIC access control

This adds basic access control to the IOAPIC. Based on the IRQ chip
configuration, we permit or deny writing to redirection table entries.
This may require integration with interrupt remapping later on.

We furthermore allow reads from other valid IOAPIC registers but deny
any other write accesses.

EOI writing is currently passed through. This will have to be revisited
as well when interrupt remapping is added.

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