ARM: 7140/1: remove NR_IRQS dependency for ARM-specific HARDIRQ_BITS definition

As a first step towards removing NR_IRQS, remove the ARM customization
of HARDIRQ_BITS based on NR_IRQS.

The generic code in <linux/hardirq.h> already has a default value of
10 for HARDIRQ_BITS which is the max used on ARM, so let's just remove
the NR_IRQS based customization and use the generic default.

Signed-off-by: Kevin Hilman <khilman@ti.com>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>