x86: io_apic: Split setup_ioapic_ids_from_mpc()

Sodaville needs to setup the IO_APIC ids as the boot loader leaves
them uninitialized. Split out the setter function so it can be called
unconditionally from the sodaville board code.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <20101126165020.GA26361@www.tglx.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>