ARM: remove mx31pdk_defconfig

This machine is enabled in mx3_defconfig and so mx31pdk_defconfig isn't
really useful.
Signed-off-by: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>

arch/arm/configs/mx31pdk_defconfig

-# CONFIG_LOCALVERSION_AUTO is not set
-# CONFIG_SWAP is not set
-# CONFIG_CC_OPTIMIZE_FOR_SIZE is not set
-# CONFIG_COMPAT_BRK is not set
-# CONFIG_IOSCHED_DEADLINE is not set
-# CONFIG_IOSCHED_CFQ is not set
-CONFIG_ARCH_MXC=y
-# CONFIG_MACH_MX31ADS is not set
-CONFIG_MACH_MX31_3DS=y
-CONFIG_AEABI=y
-CONFIG_NET=y
-CONFIG_PACKET=y
-CONFIG_UNIX=y
-CONFIG_NET_KEY=y
-CONFIG_INET=y
-CONFIG_IP_PNP=y
-CONFIG_IP_PNP_DHCP=y
-# CONFIG_INET_LRO is not set
-CONFIG_UEVENT_HELPER_PATH="/sbin/hotplug"
-# CONFIG_PREVENT_FIRMWARE_BUILD is not set
-# CONFIG_FIRMWARE_IN_KERNEL is not set
-# CONFIG_BLK_DEV is not set
-# CONFIG_MISC_DEVICES is not set
-CONFIG_NETDEVICES=y
-CONFIG_NET_ETHERNET=y
-# CONFIG_INPUT_MOUSEDEV_PSAUX is not set
-# CONFIG_INPUT_KEYBOARD is not set
-# CONFIG_INPUT_MOUSE is not set
-# CONFIG_SERIO is not set
-# CONFIG_DEVKMEM is not set
-CONFIG_SERIAL_IMX=y
-CONFIG_SERIAL_IMX_CONSOLE=y
-# CONFIG_LEGACY_PTYS is not set
-# CONFIG_HW_RANDOM is not set
-# CONFIG_HWMON is not set
-# CONFIG_VGA_CONSOLE is not set
-# CONFIG_HID_SUPPORT is not set
-# CONFIG_USB_SUPPORT is not set
-# CONFIG_DNOTIFY is not set
-# CONFIG_ENABLE_WARN_DEPRECATED is not set
-# CONFIG_ENABLE_MUST_CHECK is not set
-# CONFIG_RCU_CPU_STALL_DETECTOR is not set
-# CONFIG_CRYPTO_ANSI_CPRNG is not set
-# CONFIG_CRC32 is not set