Patch from Christoph Hellwig to:
- irq_desc and irq_to_vector machvecs.  SN2 has it's own versions,
  but they're the same as the generic ones
- kill do do_IRQ and use __do_IRQ directly everywhere
- kill dead X86 ifdefs
- move some variable declarations around in irq.c to recuce # of ifdefs
Signed-off-by: Tony Luck <tony.luck@intel.com>