x86: ordering functions in io_apic_32.c

prepare for unification:

try to make functions be of the same order to io_apic_64.c.

v2: add calling setup_msi_irq back to arch_setup_msi_irq

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>