[IA64] remove CONFIG_SMP ifdef in ia64_send_ipi()

When !CONFIG_SMP, cpu_physical_id() is ia64_get_lid(), which is
functionally identical to

    (ia64_getreg(_IA64_REG_CR_LID) >> 16) & 0xffff

so there's no need for two versions of this code.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>