CPU setup code changes:

 - Clean up & simplify AP exception handling setup.

 - Consolidate the disjoint IDT setup code living in
   idt_setup_traps() and idt_setup_ist_traps() into
   a single idt_setup_traps() initialization function
   and call it before cpu_init().

Signed-off-by: Ingo Molnar <mingo@kernel.org>