ARM: OMAP1: kconfig: Enable IRQ_DOMAIN by default for OMAP1 platforms

The devices that can act as an interrupt controller like the
GPIO are going to be handled using the IRQ domain mechanism
in order to avoid the static IRQ mapping done so far inside
plat-omap/irqs.h.

Enable IRQ_DOMAIN by default to allow the drivers shared with
OMAP2+ to compile properly on OMAP1 platforms.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Cc: Tony Lindgren <tony@atomide.com>