ARM: OMAP2+: gpmc: Modify interrupt handling

Modify interrupt handling such that interrupts can be handled by GPMC
client drivers using standard interrupt APIs rather than requiring
the drivers to have knowledge about GPMC interrupt handling. Currently
only NAND related interrupts has been considered (which is the case
even without this change) as the only user of GPMC interrupt is NAND.

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>