doc: boards: cc3220sf_launchxl: Document limitations
doc: boards: cc3220sf_launchxl: Document limitations

Adding a section on some features that have yet to be implemented in
the SimpleLink WiFi driver.

Signed-off-by: Vincent Wan <0da4a49376daf88459b96a63301ecd5aff2f3b80@linaro.org>

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