ARM: ep93xx: add GPIO I2C to defconfig

Some of the EP93xx boards have I2C devices on bit-banged GPIO
I2C, so add this to the defconfig.

Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>