ARM: 7240/1: Make ARCH_NR_GPIO a Kconfig variable

Change ARCH_NR_GPIO into a Kconfig variable as suggested by Russel King.
This makes ARCH_NR_GPIO single zImage friendly. The default value for
tegra is defined as well.

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