pc99: Explicit error for num_ioapics == 0

This is needed as otherwise the error condition will try and say that the requested ioapic
was outside the range of 0-UINT_MAX due to num_ioapics-1 underflowing.

Share linker.h between architectures

In xAPIC (P4 and above) 256 ID is availabe on system bus while in APIC serial bus only 16 ID available.
Don't check I/O APIC IDs for xAPIC systems in 32bit system.

SELFOUR-624: remove redundancy in io.[c|h]

And clean up a bit while we are there

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

x86: Fix compile assert

x86: Do not conditionally compile IRQ controller code, use build/run time checks

Guarding code with #ifdef's makes even cursor testing of 'does this code compile'
difficult due to code being hidden by the pre-processor. Using config_set in
regular C if statements is performant as the compiler can trivially detect
dead code at compile time, and at -O1 and above will not even link in symbols
referenced by dead code in these blocks, so this will not bloat image size

x86: Strip multi kernel support from the x86 kernel. This is not used and is conflicting with planned future features

Change types from uint32_t->word_t to be 32/64bit agnostic

Rationalize standard types

This commit aims to rationalize how we represent different types
for compatiblity between ARM and x86, as well as between 32 and
64 bit code. The choices being made here is to declare that a
uint32_t has a type of 'int', this allows uint32_t to be declared
consistently across 32 and 64 bit (at least in GCC).
The word_t type is declared using a 'long' (not a uint32_t or uint64_t) to
allow for a word_t to be backed by the same type on both 32 and 64 bit
All other types that want to be declared as the size of a native word
get declared in terms of a word_t

x86: Fix printing when the ioapic is enabled

xIntroduce RELEASE_PRINTF, which allows a renamed printf (release_printf) to be used in a release build of the kernel - userful for debugging tests that only fail on a release build of the kernel

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