x86: Cleanup irq_domain ops

We have 3 identical copies of the ioapic domain ops for acpi, mpparse,
and sfi. Have a global one in the io_apic code and be done with it.

To avoid include hell in io_apic.h, create a private irqdomain header
and include the generic irqdomain header from there.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: x86@kernel.org