x86: ioapic: Implement and use io_apic_setup_irq_pin_once()

io_apic_set_pci_routing() and mp_save_irq() check the pin_programmed
bit before calling io_apic_setup_irq_pin() and set the bit when the
pin was setup.

Move that duplicated code into a separate function and use it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>