MIPS: MTX-1: Update defconfig

Updates the 4G Systems MTX-1 defconfig, and remove systems unavailable
on this platform.  Changes include:

- built-in MTD char/block support
- GPIO sysfs support
- MTX-1 watchdog driver
- I2C over GPIO driver as a module
- SquashFS support

Signed-off-by: Florian Fainelli <florian@openwrt.org>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/1168/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>