ARM: OMAP2+: board-generic: Add missing handle_irq callbacks

The following commit: 6b2f55d7,
is adding the support for the CONFIG_MULTI_IRQ_HANDLER but did
not update all the machine descriptors supported in the DT
board-generic.c file.
It thus break the DT boot on OMAP3 and OMAP4 boards.

Add the proper handle_irq callbacks for OMAP3 and OMAP4 generic
machine descriptors.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>