x86: IOAPIC/MSI syscalls

Restructure the x86 interrupt handling to allow for a more flexible
method of using IOAPIC and MSI interrupts. The essence of this change
is to allow for the user to pick, for both IOAPIC and MSIs, which
CPU vector to use. Additionally there is future support, in the API,
for seL4 to eventually protect MSI interrupts with the vt-d interrupt
routing tables.

API behaviour for legacy systems using the PIC is preserved

Part of SELFOUR-281

SELFOUR-114: remove duplication of seL4_MessageInfo_t, adjust naming to avoid cparser mangling

unsigned int -> word_t

ioapic: refactored C code and first attempt at haskell spec

Support IOAPIC on ia32 and modify interrupt handling to support user level setting of modes

Release snapshot