ARM: OMAP: use edge/level handlers from generic IRQ framework

Currently, the GPIO interrupt handling is duplicating some of the work
done by the generic IRQ handlers (handle_edge_irq, handle_level_irq)
such as detecting nesting, handling re-triggers etc.  Remove this
duplication and use generic hooks based on IRQ type.

Using generic IRQ handlers ensures correct behavior when using
threaded interrupts introduced by the -rt patch.

Signed-off-by: Kevin Hilman <khilman@mvista.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>