ARM: mxs_defconfig: Turn off CONFIG_DEBUG_GPIO

Having CONFIG_DEBUG_GPIO=y leads to several debug messages polluting kernel log:

[    0.580325] of_get_named_gpio_flags: can't parse gpios property of node '/regulators/3p3v[0]'
[    0.581185] 3P3V: 3300 mV
[    0.584827] of_get_named_gpio_flags exited with status 124
[    0.585852] vddio-sd0: 3300 mV
[    0.590023] of_get_named_gpio_flags exited with status 79
[    0.590770] fec-3v3: 3300 mV
[    0.594805] of_get_named_gpio_flags exited with status 105
[    0.595491] usb0_vbus: 5000 mV
[    0.599687] of_get_named_gpio_flags exited with status 104
[    0.600380] usb1_vbus: 5000 mV
[    0.604463] of_get_named_gpio_flags exited with status 126
[    0.605153] lcd-3v3: 3300 mV
[    0.608970] of_get_named_gpio_flags exited with status 77

Turn this option off, as these messages are not really useful for normal usage.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>