Code originally by James Cleverdon.

This abstracts out some sections that were switched by
clustered_apic_mode into the following functions:

 - apic_id_registered()
 - init_apic_ldr()
 - multi_timer_check()

Changes the return check in balance_irq from testing clustered_apic_mode
to testing "no_balance_irq" to be more general.

The removal of:
	entry.dest.logical.logical_dest = TARGET_CPUS;
is because it's a duplicate (we do it twice in the same function for
no reason).