x86: ioapic: Cleanup sparse irq code

Switch over to the new allocator and remove all the magic which was
caused by the unability to destroy irq descriptors. Get rid of the
create_irq_nr() loop for sparse and non sparse irq.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@elte.hu>