[IA64] Fix some section mismatch errors

Section mismatch: reference to ...

 .init.text:prefill_possible_map from .text between 'setup_per_cpu_areas' and 'cpu_init'
 .init.text:iosapic_override_isa_irq from .text between 'iosapic_init' and 'iosapic_remove'

Signed-off-by: Tony Luck <tony.luck@intel.com>