arm: irq: Remove check for hardirq mask size

SPARSE_IRQ gives the freedom to use high, discontiguous IRQ
numbers at very low memory costs. But even with SPARSE_IRQ, the
highest interrupt number of the system is limited by NR_IRQS,
since NR_IRQS defines the number of IRQ_BITMAP_BITS.

NR_IRQS is currently limited to 1024 on ARM, as of the following
commit:

commit 5a5fb7d
Author: Steven Rostedt <srostedt@redhat.com>
Date:   Thu Feb 12 10:53:37 2009 -0500

    preempt-count: force hardirq-count to max of 10

This implies that architectures having more than 1024 interrupts
cannot manage. Let's remove the constraint on nesting level,
since as the commit above mentions, we're probably bound by stack
size at that point, anyways.