ARM: 7241/1: mach-ux500 Use CONFIG_ARCH_NR_GPIO

Add default value for CONFIG_ARCH_NR_GPIO to Kconfig and remove the
definition in gpio.h. We can't remove gpio.h yet as asm/gpio.h still
includes it.

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>