samples: SMF: LVGL: SMF-based Calculator

This sample crates a touchscreen desk calculator based on
the sample state machine in _Practical UML Statecharts in
C/C++_ by Miro Samek.

Sample should build and run on any touchscreen-enabled
board with sufficient resources.

Tested on `disco_l475_iot1` board with
`adafruit_2_8_tft_touch_v2` touchscreen.

Signed-off-by: Glenn Andrews <glenn.andrews.42@gmail.com>