xiaomi-santoni: Added support for osk-sdl and improvements

I've added support for osk-sdl to the xiaomi-santoni, it works fine, charging-sdl works fine, but full disk encryption doesn't work yet. Here is charging-sdl running:

device/device-xiaomi-santoni/100-charging.rules

+SUBSYSTEM=="power_supply", ATTRS{type}=="Battery", ATTRS{status}=="Charging", RUN+="/usr/lib/device-xiaomi-santoni/charging.sh"
+SUBSYSTEM=="power_supply", ATTRS{type}=="Battery", ATTRS{status}=="Discharging", RUN+="/usr/lib/device-xiaomi-santoni/discharging.sh"