M68k irq updates (most from Roman Zippel):
  - Update m68k to new irq API in 2.5.29
  - synchronize_irq() takes a parameter now
  - Remove obsolete definitions
  - Avoid too much inline assembly in __xchg
  - Add irqs_disabled(), which appeared in 2.5.34
  - Add missing implementation for in_atomic() (introduced in 2.5.35)