x86: consolidate SMP code in io_apic.c

Impact: Cleanup

Reorganizes the code in arch/x86/kernel/io_apic.c by
combining two '#ifdef CONFIG_SMP' regions.  In addition
to making the code easier to understand the first
'#ifdef CONFIG_SMP' region is moved to a location later
in the file which will reduce the need for function
forward declarations when the code subsequently revised.

The only changes other than relocating code to a different
position in the file were the removal of the assign_irq_vector()
forward declaration which was no longer needed and some line
length reduction formatting changes.

Signed-off-by: Gary Hade <garyhade@us.ibm.com>
Cc: lcm@us.ibm.com
LKML-Reference: <20090408210725.GC11159@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>