People are playing odd games with IRQF_DISABLED, remove it.

Its not reliable, since shared interrupt lines could disable it for you,
and its possible and allowed for archs to disable IRQs to limit IRQ nesting.

Therefore, simply mandate that _ALL_ IRQ handlers are run with IRQs disabled.

[ This _should_ not break anything, since we've mandated that IRQ handlers
  _must_ be able to deal with this for a _long_ time ]

IRQ handlers should be fast, no if buts and any other exceptions. We also have
plenty instrumentation to find any offending IRQ latency sources.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NHelge Deller <deller@gmx.de>