config: drop CONFIG_DEBUG_GPIO

on my Wandboard Quad dmesg for kernel 3.12 shows messages like
[ 2.001931] of_get_named_gpio_flags: can't parse gpios property of node '/regulators/2p5v[0]'

Fabio Estevam wrote to me:
In order to silence these debug messages: just unselect
CONFIG_DEBUG_GPIO from the defconfig and they will not show up anymore.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Robert Nelson <robertcnelson@gmail.com>