ACPI / ia64: introduce variable acpi_lapic into ia64

This variable was defined and assigned in x86, is used to indicate
whether LAPIC exists in MADT. Now introduce it into ia64 to help
make correct judgment when get information for ACPI processor later.

Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>