[MIPS] use generic_handle_irq, handle_level_irq, handle_percpu_irq

Further incorporation of generic irq framework.  Replacing __do_IRQ()
by proper flow handler would make the irq handling path a bit simpler
and faster.

* use generic_handle_irq() instead of __do_IRQ().
* use handle_level_irq for obvious level-type irq chips.
* use handle_percpu_irq for irqs marked as IRQ_PER_CPU.
* setup .eoi routine for irq chips possibly used with handle_percpu_irq.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>