arm: omap: irq: use IRQCHIP_DECLARE macro

IRQCHIP_DECLARE macro is used to declare the same
of_device_id structure for irqchips, it's just
a helper. No functional changes.

Note that we're temporarily including irqchip.h
with its full path, until we move this driver
to drivers/irqchip/.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>