arm: omap: irq: get rid of ifdef hack

we don't need the ifdef if we have omap_nr_pending
telling us how many pending registers we have
on current platform. This solves a possible
problem where we could try to handle bogus
interrupts on OMAP2 and OMAP3 if using single
zImage kernel, because we would end up reading
the following pending FIQ register.

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