drivers: i2c: add missing I2C_GECKO Kconfig option
drivers: i2c: add missing I2C_GECKO Kconfig option

This commit adds missing I2C_GECKO Kconfig option which currently is
being set implicitly via .defconfig file.

Signed-off-by: Piotr Mienkowski <be7d9ab625d3cb5e3a4a3202f3529b954dba084c@gmail.com>

Vudentz/zephyr,ldts/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,galak/zephyr,nashif/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,nashif/zephyr,ldts/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,punitvara/zephyr,nashif/zephyr,ldts/zephyr,galak/zephyr,punitvara/zephyr,nashif/zephyr,Vudentz/zephyr,explora26/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,punitvara/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr