Revert "arm: irq: Allow for specification of no preallocated irqs"

This reverts commit 0bb2b56f.

This change is no longer necessary as of the following change,
since now we only preallocate 16 IRQs for SPARSE_IRQ
configurations. Thus the original problem of the system wasting
descriptions due to preallocated irqs no longer exists.

Author: Rob Herring <rob.herring@calxeda.com>
Date:   Tue Jan 3 15:17:23 2012 -0600

    ARM: only include mach/irqs.h for !SPARSE_IRQ

This also reverts commit ce4b20b3.

Since the preallocation scheme has been removed, we need to
update the board file to remove the old preallocation
specification.

Change-Id: I8fd819ae81fa0c8276877c0614653b5e5e14b3e2
Signed-off-by: Michael Bohan <mbohan@codeaurora.org>