remove extern declaration of handle_IPI() in irq_ia64.c.
Instead, declare it in asm-ia64/smp.h.
Later handle_IPI() will be referenced from another file.
Signed-off-by: NIsaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: NTony Luck <tony.luck@intel.com>