ARM: 6200/1: AT91: Define NR_BUILTIN_GPIO

Add definition for NR_BUILTIN_GPIO for AT91 family

Signed-off-by: Ryan Mallon <ryan@bluewatersys.com>
Acked-by: Andrew Victor <linux@maxim.org.za>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>